diff --git a/migrations/2024_01_01_000001_improve_transactions_table.php b/migrations/2024_01_01_000001_improve_transactions_table.php
new file mode 100644
index 0000000..1570c3e
--- /dev/null
+++ b/migrations/2024_01_01_000001_improve_transactions_table.php
@@ -0,0 +1,205 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Schema;
+
+/**
+ * Improve the transactions table to serve as the platform-wide financial
+ * transaction primitive.
+ *
+ * Changes:
+ *  - Rename owner_uuid/owner_type  → subject_uuid/subject_type
+ *  - Add payer_uuid/payer_type     (who the money flows from)
+ *  - Add payee_uuid/payee_type     (who the money flows to)
+ *  - Add initiator_uuid/initiator_type (what triggered the transaction)
+ *  - Add context_uuid/context_type (related business object)
+ *  - Add direction (credit|debit)
+ *  - Add balance_after (running balance snapshot, wallet context)
+ *  - Add fee_amount, tax_amount, net_amount (monetary breakdown)
+ *  - Add exchange_rate, settled_currency, settled_amount (multi-currency)
+ *  - Add reference (idempotency key, unique)
+ *  - Add parent_transaction_uuid (refund/reversal/split linkage)
+ *  - Add gateway_response JSON (raw gateway payload)
+ *  - Add payment_method, payment_method_last4, payment_method_brand
+ *  - Add ip_address (fraud/audit trail)
+ *  - Add notes (internal operator annotation)
+ *  - Add failure_reason, failure_code (structured failure info)
+ *  - Add period (YYYY-MM accounting period, denormalised)
+ *  - Add tags JSON (operator-defined categorisation)
+ *  - Add settled_at, voided_at, reversed_at, expires_at timestamps
+ *  - Make amount NOT NULL DEFAULT 0
+ *  - Keep customer_uuid/customer_type as deprecated nullable aliases
+ *  - Keep owner_uuid/owner_type as deprecated nullable aliases (backfilled)
+ */
+return new class extends Migration {
+    public function up(): void
+    {
+        Schema::table('transactions', function (Blueprint $table) {
+            // ----------------------------------------------------------------
+            // New polymorphic: subject (primary owner of the transaction record)
+            // ----------------------------------------------------------------
+            $table->char('subject_uuid', 36)->nullable()->after('owner_type');
+            $table->string('subject_type')->nullable()->after('subject_uuid');
+
+            // ----------------------------------------------------------------
+            // New polymorphic: payer (funds flow from)
+            // ----------------------------------------------------------------
+            $table->char('payer_uuid', 36)->nullable()->after('subject_type');
+            $table->string('payer_type')->nullable()->after('payer_uuid');
+
+            // ----------------------------------------------------------------
+            // New polymorphic: payee (funds flow to)
+            // ----------------------------------------------------------------
+            $table->char('payee_uuid', 36)->nullable()->after('payer_type');
+            $table->string('payee_type')->nullable()->after('payee_uuid');
+
+            // ----------------------------------------------------------------
+            // New polymorphic: initiator (what triggered the transaction)
+            // ----------------------------------------------------------------
+            $table->char('initiator_uuid', 36)->nullable()->after('payee_type');
+            $table->string('initiator_type')->nullable()->after('initiator_uuid');
+
+            // ----------------------------------------------------------------
+            // New polymorphic: context (related business object)
+            // ----------------------------------------------------------------
+            $table->char('context_uuid', 36)->nullable()->after('initiator_type');
+            $table->string('context_type')->nullable()->after('context_uuid');
+
+            // ----------------------------------------------------------------
+            // Direction and balance
+            // ----------------------------------------------------------------
+            $table->string('direction')->nullable()->after('status');  // credit | debit
+            $table->integer('balance_after')->nullable()->after('direction');
+
+            // ----------------------------------------------------------------
+            // Monetary breakdown (all in smallest currency unit / cents)
+            // ----------------------------------------------------------------
+            $table->integer('fee_amount')->default(0)->after('amount');
+            $table->integer('tax_amount')->default(0)->after('fee_amount');
+            $table->integer('net_amount')->default(0)->after('tax_amount');
+
+            // ----------------------------------------------------------------
+            // Multi-currency settlement
+            // ----------------------------------------------------------------
+            $table->decimal('exchange_rate', 18, 8)->default(1)->after('currency');
+            $table->string('settled_currency', 3)->nullable()->after('exchange_rate');
+            $table->integer('settled_amount')->nullable()->after('settled_currency');
+
+            // ----------------------------------------------------------------
+            // Idempotency and linkage
+            // ----------------------------------------------------------------
+            $table->string('reference', 191)->nullable()->unique()->after('description');
+            $table->char('parent_transaction_uuid', 36)->nullable()->after('reference');
+
+            // ----------------------------------------------------------------
+            // Gateway enrichment
+            // ----------------------------------------------------------------
+            $table->json('gateway_response')->nullable()->after('gateway_transaction_id');
+            $table->string('payment_method', 50)->nullable()->after('gateway_response');
+            $table->string('payment_method_last4', 4)->nullable()->after('payment_method');
+            $table->string('payment_method_brand', 50)->nullable()->after('payment_method_last4');
+
+            // ----------------------------------------------------------------
+            // Traceability and compliance
+            // ----------------------------------------------------------------
+            $table->string('ip_address', 45)->nullable()->after('meta');
+            $table->text('notes')->nullable()->after('ip_address');
+            $table->string('failure_reason', 191)->nullable()->after('notes');
+            $table->string('failure_code', 50)->nullable()->after('failure_reason');
+
+            // ----------------------------------------------------------------
+            // Reporting
+            // ----------------------------------------------------------------
+            $table->string('period', 7)->nullable()->after('failure_code');   // YYYY-MM
+            $table->json('tags')->nullable()->after('period');
+
+            // ----------------------------------------------------------------
+            // Lifecycle timestamps
+            // ----------------------------------------------------------------
+            $table->timestamp('settled_at')->nullable()->after('updated_at');
+            $table->timestamp('voided_at')->nullable()->after('settled_at');
+            $table->timestamp('reversed_at')->nullable()->after('voided_at');
+            $table->timestamp('expires_at')->nullable()->after('reversed_at');
+        });
+
+        // --------------------------------------------------------------------
+        // Backfill subject_* from owner_* (preserve existing data)
+        // --------------------------------------------------------------------
+        DB::statement('UPDATE transactions SET subject_uuid = owner_uuid, subject_type = owner_type WHERE owner_uuid IS NOT NULL');
+
+        // --------------------------------------------------------------------
+        // Backfill payer_* from customer_* (customer was semantically the payer)
+        // --------------------------------------------------------------------
+        DB::statement('UPDATE transactions SET payer_uuid = customer_uuid, payer_type = customer_type WHERE customer_uuid IS NOT NULL');
+
+        // --------------------------------------------------------------------
+        // Backfill period from created_at
+        // --------------------------------------------------------------------
+        DB::statement("UPDATE transactions SET period = DATE_FORMAT(created_at, '%Y-%m') WHERE created_at IS NOT NULL");
+
+        // --------------------------------------------------------------------
+        // Backfill net_amount = amount (no fees/tax in legacy records)
+        // --------------------------------------------------------------------
+        DB::statement('UPDATE transactions SET net_amount = COALESCE(amount, 0) WHERE net_amount = 0');
+
+        // --------------------------------------------------------------------
+        // Add indexes on new columns
+        // --------------------------------------------------------------------
+        Schema::table('transactions', function (Blueprint $table) {
+            $table->index(['subject_uuid', 'subject_type'], 'transactions_subject_index');
+            $table->index(['payer_uuid', 'payer_type'], 'transactions_payer_index');
+            $table->index(['payee_uuid', 'payee_type'], 'transactions_payee_index');
+            $table->index(['initiator_uuid', 'initiator_type'], 'transactions_initiator_index');
+            $table->index(['context_uuid', 'context_type'], 'transactions_context_index');
+            $table->index('direction', 'transactions_direction_index');
+            $table->index('period', 'transactions_period_index');
+            $table->index('parent_transaction_uuid', 'transactions_parent_index');
+            $table->index('payment_method', 'transactions_payment_method_index');
+            $table->index('settled_at', 'transactions_settled_at_index');
+            $table->index(['company_uuid', 'type'], 'transactions_company_type_index');
+            $table->index(['company_uuid', 'status'], 'transactions_company_status_index');
+            $table->index(['company_uuid', 'period'], 'transactions_company_period_index');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('transactions', function (Blueprint $table) {
+            // Drop indexes
+            $table->dropIndex('transactions_subject_index');
+            $table->dropIndex('transactions_payer_index');
+            $table->dropIndex('transactions_payee_index');
+            $table->dropIndex('transactions_initiator_index');
+            $table->dropIndex('transactions_context_index');
+            $table->dropIndex('transactions_direction_index');
+            $table->dropIndex('transactions_period_index');
+            $table->dropIndex('transactions_parent_index');
+            $table->dropIndex('transactions_payment_method_index');
+            $table->dropIndex('transactions_settled_at_index');
+            $table->dropIndex('transactions_company_type_index');
+            $table->dropIndex('transactions_company_status_index');
+            $table->dropIndex('transactions_company_period_index');
+            $table->dropUnique(['reference']);
+
+            // Drop new columns
+            $table->dropColumn([
+                'subject_uuid', 'subject_type',
+                'payer_uuid', 'payer_type',
+                'payee_uuid', 'payee_type',
+                'initiator_uuid', 'initiator_type',
+                'context_uuid', 'context_type',
+                'direction', 'balance_after',
+                'fee_amount', 'tax_amount', 'net_amount',
+                'exchange_rate', 'settled_currency', 'settled_amount',
+                'reference', 'parent_transaction_uuid',
+                'gateway_response',
+                'payment_method', 'payment_method_last4', 'payment_method_brand',
+                'ip_address', 'notes', 'failure_reason', 'failure_code',
+                'period', 'tags',
+                'settled_at', 'voided_at', 'reversed_at', 'expires_at',
+            ]);
+        });
+    }
+};
diff --git a/migrations/2024_01_01_000002_improve_transaction_items_table.php b/migrations/2024_01_01_000002_improve_transaction_items_table.php
new file mode 100644
index 0000000..8066f19
--- /dev/null
+++ b/migrations/2024_01_01_000002_improve_transaction_items_table.php
@@ -0,0 +1,70 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Schema;
+
+/**
+ * Improve the transaction_items table to align with the robust transaction
+ * primitive design.
+ *
+ * Changes:
+ *  - Add public_id (HasPublicId support)
+ *  - Fix amount column type: string → INT NOT NULL DEFAULT 0
+ *  - Add quantity (INT DEFAULT 1)
+ *  - Add unit_price (INT DEFAULT 0, cents)
+ *  - Add tax_rate (DECIMAL(5,2) DEFAULT 0.00)
+ *  - Add tax_amount (INT DEFAULT 0, cents)
+ *  - Add description (longer text alternative to details)
+ *  - Add sort_order (for ordered line item display)
+ */
+return new class extends Migration {
+    public function up(): void
+    {
+        Schema::table('transaction_items', function (Blueprint $table) {
+            // Add public_id for HasPublicId trait support
+            $table->string('public_id', 191)->nullable()->unique()->after('uuid');
+
+            // Add quantity and unit price for proper line-item accounting
+            $table->integer('quantity')->default(1)->after('transaction_uuid');
+            $table->integer('unit_price')->default(0)->after('quantity');
+
+            // Add tax columns
+            $table->decimal('tax_rate', 5, 2)->default(0.00)->after('currency');
+            $table->integer('tax_amount')->default(0)->after('tax_rate');
+
+            // Add description as a longer alternative to details (TEXT vs VARCHAR)
+            $table->text('description')->nullable()->after('details');
+
+            // Add sort order for ordered display of line items
+            $table->unsignedSmallInteger('sort_order')->default(0)->after('description');
+        });
+
+        // Fix amount column: string → integer
+        // First copy to a temp column, then drop and re-add as integer
+        DB::statement('ALTER TABLE transaction_items MODIFY COLUMN amount BIGINT NOT NULL DEFAULT 0');
+
+        // Backfill unit_price = amount for existing records (single-unit assumption)
+        DB::statement('UPDATE transaction_items SET unit_price = amount WHERE unit_price = 0 AND amount > 0');
+    }
+
+    public function down(): void
+    {
+        // Revert amount back to string (original type)
+        DB::statement('ALTER TABLE transaction_items MODIFY COLUMN amount VARCHAR(191) NULL');
+
+        Schema::table('transaction_items', function (Blueprint $table) {
+            $table->dropUnique(['public_id']);
+            $table->dropColumn([
+                'public_id',
+                'quantity',
+                'unit_price',
+                'tax_rate',
+                'tax_amount',
+                'description',
+                'sort_order',
+            ]);
+        });
+    }
+};
diff --git a/src/Models/Transaction.php b/src/Models/Transaction.php
index b10e169..2a5a1aa 100644
--- a/src/Models/Transaction.php
+++ b/src/Models/Transaction.php
@@ -3,13 +3,38 @@
 namespace Fleetbase\Models;
 
 use Fleetbase\Casts\Json;
+use Fleetbase\Casts\Money;
 use Fleetbase\Casts\PolymorphicType;
 use Fleetbase\Traits\HasApiModelBehavior;
 use Fleetbase\Traits\HasApiModelCache;
 use Fleetbase\Traits\HasMetaAttributes;
 use Fleetbase\Traits\HasPublicId;
 use Fleetbase\Traits\HasUuid;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\HasMany;
+use Illuminate\Database\Eloquent\Relations\MorphTo;
+use Illuminate\Database\Eloquent\SoftDeletes;
 
+/**
+ * Transaction
+ *
+ * The platform-wide financial transaction primitive. Every monetary movement
+ * on the Fleetbase platform — dispatch charges, wallet operations, gateway
+ * payments, refunds, earnings, adjustments — is recorded as a Transaction.
+ *
+ * Extensions (e.g. Ledger) extend this model to add domain-specific
+ * relationships (journal entries, invoices) without altering this schema.
+ *
+ * Monetary values are always stored as integers in the smallest currency unit
+ * (cents). For example, USD 10.50 is stored as 1050.
+ *
+ * Five polymorphic roles capture the full context of any transaction:
+ *   - subject:   the primary owner of the transaction record
+ *   - payer:     the entity funds flow FROM
+ *   - payee:     the entity funds flow TO
+ *   - initiator: what triggered or authorised the transaction
+ *   - context:   the related business object (Order, Invoice, etc.)
+ */
 class Transaction extends Model
 {
     use HasUuid;
@@ -17,85 +42,470 @@ class Transaction extends Model
     use HasApiModelBehavior;
     use HasApiModelCache;
     use HasMetaAttributes;
+    use SoftDeletes;
 
     /**
      * The database table used by the model.
-     *
-     * @var string
      */
     protected $table = 'transactions';
 
     /**
-     * The type of public Id to generate.
-     *
-     * @var string
+     * The type of public ID to generate.
      */
     protected $publicIdType = 'transaction';
 
     /**
-     * The attributes that can be queried.
-     *
-     * @var array
+     * The attributes that can be queried via search.
      */
-    protected $searchableColumns = [];
+    protected $searchableColumns = ['description', 'reference', 'gateway_transaction_id', 'type', 'status'];
 
     /**
      * The attributes that are mass assignable.
-     *
-     * @var array
      */
-    protected $fillable = ['public_id', 'owner_uuid', 'owner_type', 'customer_uuid', 'customer_type', 'company_uuid', 'gateway_transaction_id', 'gateway', 'gateway_uuid', 'amount', 'currency', 'description', 'meta', 'type', 'status'];
+    protected $fillable = [
+        'public_id',
+        'company_uuid',
+
+        // Five polymorphic roles
+        'subject_uuid',
+        'subject_type',
+        'payer_uuid',
+        'payer_type',
+        'payee_uuid',
+        'payee_type',
+        'initiator_uuid',
+        'initiator_type',
+        'context_uuid',
+        'context_type',
+
+        // Classification
+        'type',
+        'direction',
+        'status',
+
+        // Monetary (all in smallest currency unit / cents)
+        'amount',
+        'fee_amount',
+        'tax_amount',
+        'net_amount',
+        'currency',
+        'exchange_rate',
+        'settled_currency',
+        'settled_amount',
+        'balance_after',
+
+        // Gateway
+        'gateway',
+        'gateway_uuid',
+        'gateway_transaction_id',
+        'gateway_response',
+        'payment_method',
+        'payment_method_last4',
+        'payment_method_brand',
+
+        // Idempotency and linkage
+        'reference',
+        'parent_transaction_uuid',
+
+        // Descriptive
+        'description',
+        'notes',
+
+        // Failure info
+        'failure_reason',
+        'failure_code',
+
+        // Reporting
+        'period',
+        'tags',
+
+        // Traceability
+        'ip_address',
+
+        // Misc
+        'meta',
+
+        // Deprecated aliases (kept for backward compatibility)
+        'owner_uuid',
+        'owner_type',
+        'customer_uuid',
+        'customer_type',
+    ];
 
     /**
-     * Dynamic attributes that are appended to object.
-     *
-     * @var array
+     * The attributes that should be cast to native types.
+     */
+    protected $casts = [
+        'amount'           => Money::class,
+        'fee_amount'       => Money::class,
+        'tax_amount'       => Money::class,
+        'net_amount'       => Money::class,
+        'balance_after'    => Money::class,
+        'settled_amount'   => Money::class,
+        'exchange_rate'    => 'decimal:8',
+        'gateway_response' => Json::class,
+        'tags'             => Json::class,
+        'meta'             => Json::class,
+        'subject_type'     => PolymorphicType::class,
+        'payer_type'       => PolymorphicType::class,
+        'payee_type'       => PolymorphicType::class,
+        'initiator_type'   => PolymorphicType::class,
+        'context_type'     => PolymorphicType::class,
+        'customer_type'    => PolymorphicType::class,
+        'settled_at'       => 'datetime',
+        'voided_at'        => 'datetime',
+        'reversed_at'      => 'datetime',
+        'expires_at'       => 'datetime',
+    ];
+
+    /**
+     * Dynamic attributes appended to the model's JSON form.
      */
     protected $appends = [];
 
     /**
      * The attributes excluded from the model's JSON form.
-     *
-     * @var array
      */
-    protected $hidden = [];
+    protected $hidden = ['gateway_response'];
+
+    // =========================================================================
+    // Direction Constants
+    // =========================================================================
+
+    /** Money flowing into the subject's account. */
+    public const DIRECTION_CREDIT = 'credit';
+
+    /** Money flowing out of the subject's account. */
+    public const DIRECTION_DEBIT = 'debit';
+
+    // =========================================================================
+    // Status Constants
+    // =========================================================================
+
+    public const STATUS_PENDING   = 'pending';
+    public const STATUS_SUCCESS   = 'success';
+    public const STATUS_FAILED    = 'failed';
+    public const STATUS_REVERSED  = 'reversed';
+    public const STATUS_CANCELLED = 'cancelled';
+    public const STATUS_VOIDED    = 'voided';
+    public const STATUS_EXPIRED   = 'expired';
+
+    // =========================================================================
+    // Type Constants — Platform-wide taxonomy
+    // =========================================================================
+
+    // FleetOps
+    public const TYPE_DISPATCH      = 'dispatch';
+    public const TYPE_SERVICE_QUOTE = 'service_quote';
+
+    // Wallet operations
+    public const TYPE_WALLET_DEPOSIT      = 'wallet_deposit';
+    public const TYPE_WALLET_WITHDRAWAL   = 'wallet_withdrawal';
+    public const TYPE_WALLET_TRANSFER_IN  = 'wallet_transfer_in';
+    public const TYPE_WALLET_TRANSFER_OUT = 'wallet_transfer_out';
+    public const TYPE_WALLET_EARNING      = 'wallet_earning';
+    public const TYPE_WALLET_PAYOUT       = 'wallet_payout';
+    public const TYPE_WALLET_FEE          = 'wallet_fee';
+    public const TYPE_WALLET_ADJUSTMENT   = 'wallet_adjustment';
+    public const TYPE_WALLET_REFUND       = 'wallet_refund';
+
+    // Gateway payments
+    public const TYPE_GATEWAY_CHARGE       = 'gateway_charge';
+    public const TYPE_GATEWAY_REFUND       = 'gateway_refund';
+    public const TYPE_GATEWAY_SETUP_INTENT = 'gateway_setup_intent';
+
+    // Invoice
+    public const TYPE_INVOICE_PAYMENT = 'invoice_payment';
+    public const TYPE_INVOICE_REFUND  = 'invoice_refund';
+
+    // System
+    public const TYPE_ADJUSTMENT = 'adjustment';
+    public const TYPE_REVERSAL   = 'reversal';
+    public const TYPE_CORRECTION = 'correction';
+
+    // =========================================================================
+    // Relationships
+    // =========================================================================
+
+    /**
+     * The primary owner of this transaction record.
+     * Replaces the deprecated owner() relationship.
+     */
+    public function subject(): MorphTo
+    {
+        return $this->morphTo(__FUNCTION__, 'subject_type', 'subject_uuid')->withoutGlobalScopes();
+    }
 
     /**
-     * The attributes that should be cast to native types.
-     *
-     * @var array
+     * The entity funds flow FROM.
      */
-    protected $casts = [
-        'meta'          => Json::class,
-        'customer_type' => PolymorphicType::class,
-    ];
+    public function payer(): MorphTo
+    {
+        return $this->morphTo(__FUNCTION__, 'payer_type', 'payer_uuid')->withoutGlobalScopes();
+    }
+
+    /**
+     * The entity funds flow TO.
+     */
+    public function payee(): MorphTo
+    {
+        return $this->morphTo(__FUNCTION__, 'payee_type', 'payee_uuid')->withoutGlobalScopes();
+    }
+
+    /**
+     * What triggered or authorised this transaction.
+     */
+    public function initiator(): MorphTo
+    {
+        return $this->morphTo(__FUNCTION__, 'initiator_type', 'initiator_uuid')->withoutGlobalScopes();
+    }
+
+    /**
+     * The related business object (Order, Invoice, PurchaseRate, etc.).
+     */
+    public function context(): MorphTo
+    {
+        return $this->morphTo(__FUNCTION__, 'context_type', 'context_uuid')->withoutGlobalScopes();
+    }
+
+    /**
+     * The parent transaction this record is a refund, reversal, or split of.
+     */
+    public function parentTransaction(): BelongsTo
+    {
+        return $this->belongsTo(static::class, 'parent_transaction_uuid', 'uuid');
+    }
+
+    /**
+     * Child transactions (refunds, reversals, splits) of this transaction.
+     */
+    public function childTransactions(): HasMany
+    {
+        return $this->hasMany(static::class, 'parent_transaction_uuid', 'uuid');
+    }
+
+    /**
+     * Line items belonging to this transaction.
+     */
+    public function items(): HasMany
+    {
+        return $this->hasMany(TransactionItem::class, 'transaction_uuid', 'uuid');
+    }
 
     /**
-     * Transaction items.
-     *
-     * @var array
+     * @deprecated Use subject() instead.
      */
-    public function items()
+    public function owner(): MorphTo
     {
-        return $this->hasMany(TransactionItem::class);
+        return $this->morphTo(__FUNCTION__, 'owner_type', 'owner_uuid')->withoutGlobalScopes();
     }
 
     /**
-     * The customer if any for this place.
-     *
-     * @var Model
+     * @deprecated Use payer() instead. The customer was semantically the payer.
      */
-    public function customer()
+    public function customer(): MorphTo
     {
         return $this->morphTo(__FUNCTION__, 'customer_type', 'customer_uuid')->withoutGlobalScopes();
     }
 
+    // =========================================================================
+    // Scopes
+    // =========================================================================
+
+    /**
+     * Scope to credit transactions (money in).
+     */
+    public function scopeCredits($query)
+    {
+        return $query->where('direction', self::DIRECTION_CREDIT);
+    }
+
+    /**
+     * Scope to debit transactions (money out).
+     */
+    public function scopeDebits($query)
+    {
+        return $query->where('direction', self::DIRECTION_DEBIT);
+    }
+
+    /**
+     * Scope to successful transactions.
+     */
+    public function scopeSuccessful($query)
+    {
+        return $query->where('status', self::STATUS_SUCCESS);
+    }
+
+    /**
+     * Scope to pending transactions.
+     */
+    public function scopePending($query)
+    {
+        return $query->where('status', self::STATUS_PENDING);
+    }
+
+    /**
+     * Scope to failed transactions.
+     */
+    public function scopeFailed($query)
+    {
+        return $query->where('status', self::STATUS_FAILED);
+    }
+
+    /**
+     * Scope to a specific transaction type.
+     */
+    public function scopeOfType($query, string $type)
+    {
+        return $query->where('type', $type);
+    }
+
+    /**
+     * Scope to transactions for a specific accounting period (YYYY-MM).
+     */
+    public function scopeForPeriod($query, string $period)
+    {
+        return $query->where('period', $period);
+    }
+
+    /**
+     * Scope to transactions where the given model is the subject.
+     */
+    public function scopeForSubject($query, \Illuminate\Database\Eloquent\Model $subject)
+    {
+        return $query->where('subject_uuid', $subject->uuid)
+                     ->where('subject_type', get_class($subject));
+    }
+
+    /**
+     * Scope to transactions where the given model is the payer.
+     */
+    public function scopeForPayer($query, \Illuminate\Database\Eloquent\Model $payer)
+    {
+        return $query->where('payer_uuid', $payer->uuid)
+                     ->where('payer_type', get_class($payer));
+    }
+
+    /**
+     * Scope to transactions where the given model is the payee.
+     */
+    public function scopeForPayee($query, \Illuminate\Database\Eloquent\Model $payee)
+    {
+        return $query->where('payee_uuid', $payee->uuid)
+                     ->where('payee_type', get_class($payee));
+    }
+
+    /**
+     * Scope to transactions related to a specific business context object.
+     */
+    public function scopeForContext($query, \Illuminate\Database\Eloquent\Model $context)
+    {
+        return $query->where('context_uuid', $context->uuid)
+                     ->where('context_type', get_class($context));
+    }
+
+    /**
+     * Scope to refund/reversal transactions (children of another transaction).
+     */
+    public function scopeRefunds($query)
+    {
+        return $query->whereNotNull('parent_transaction_uuid');
+    }
+
+    // =========================================================================
+    // Helpers
+    // =========================================================================
+
+    /**
+     * Whether this transaction is a credit (money in to subject).
+     */
+    public function isCredit(): bool
+    {
+        return $this->direction === self::DIRECTION_CREDIT;
+    }
+
+    /**
+     * Whether this transaction is a debit (money out from subject).
+     */
+    public function isDebit(): bool
+    {
+        return $this->direction === self::DIRECTION_DEBIT;
+    }
+
+    /**
+     * Whether this transaction completed successfully.
+     */
+    public function isSuccessful(): bool
+    {
+        return $this->status === self::STATUS_SUCCESS;
+    }
+
+    /**
+     * Whether this transaction is still pending.
+     */
+    public function isPending(): bool
+    {
+        return $this->status === self::STATUS_PENDING;
+    }
+
+    /**
+     * Whether this transaction failed.
+     */
+    public function isFailed(): bool
+    {
+        return $this->status === self::STATUS_FAILED;
+    }
+
+    /**
+     * Whether this transaction is a refund or reversal of another transaction.
+     */
+    public function isRefund(): bool
+    {
+        return $this->parent_transaction_uuid !== null;
+    }
+
+    /**
+     * Whether this transaction has been voided.
+     */
+    public function isVoided(): bool
+    {
+        return $this->status === self::STATUS_VOIDED || $this->voided_at !== null;
+    }
+
     /**
-     * Generates a fleetbase transaction number.
-     *
-     * @var array
+     * Whether this transaction has been reversed.
      */
-    public static function generateInternalNumber($length = 10)
+    public function isReversed(): bool
+    {
+        return $this->status === self::STATUS_REVERSED || $this->reversed_at !== null;
+    }
+
+    /**
+     * Whether this transaction has settled.
+     */
+    public function isSettled(): bool
+    {
+        return $this->settled_at !== null;
+    }
+
+    /**
+     * Whether this transaction has expired (e.g. an uncaptured pre-auth).
+     */
+    public function isExpired(): bool
+    {
+        return $this->status === self::STATUS_EXPIRED ||
+               ($this->expires_at !== null && $this->expires_at->isPast());
+    }
+
+    // =========================================================================
+    // Static Helpers
+    // =========================================================================
+
+    /**
+     * Generate an internal transaction reference number.
+     * Format: TR + N random digits.
+     */
+    public static function generateInternalNumber(int $length = 10): string
     {
         $number = 'TR';
         for ($i = 0; $i < $length; $i++) {
@@ -106,18 +516,17 @@ public static function generateInternalNumber($length = 10)
     }
 
     /**
-     * Generates a unique transaction number.
-     *
-     * @var array
+     * Generate a unique transaction reference number.
+     * Ensures uniqueness against the gateway_transaction_id column.
      */
-    public static function generateNumber($length = 10)
+    public static function generateNumber(int $length = 10): string
     {
         $n  = self::generateInternalNumber($length);
-        $tr = self::where('gateway_transaction_id', $n)
-            ->withTrashed()
-            ->first();
-        while (is_object($tr) && $n == $tr->gateway_transaction_id) {
-            $n = self::generateInternalNumber($length);
+        $tr = self::where('gateway_transaction_id', $n)->withTrashed()->first();
+
+        while ($tr !== null && $n === $tr->gateway_transaction_id) {
+            $n  = self::generateInternalNumber($length);
+            $tr = self::where('gateway_transaction_id', $n)->withTrashed()->first();
         }
 
         return $n;
diff --git a/src/Models/TransactionItem.php b/src/Models/TransactionItem.php
index 0b8e957..4f6b339 100644
--- a/src/Models/TransactionItem.php
+++ b/src/Models/TransactionItem.php
@@ -3,48 +3,122 @@
 namespace Fleetbase\Models;
 
 use Fleetbase\Casts\Json;
+use Fleetbase\Casts\Money;
+use Fleetbase\Traits\HasApiModelBehavior;
 use Fleetbase\Traits\HasMetaAttributes;
+use Fleetbase\Traits\HasPublicId;
 use Fleetbase\Traits\HasUuid;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\SoftDeletes;
 
+/**
+ * TransactionItem
+ *
+ * A line item belonging to a Transaction. Stores the individual components
+ * of a transaction's total — e.g. base fare, surcharges, taxes, discounts.
+ *
+ * All monetary values (amount, unit_price, tax_amount) are stored as integers
+ * in the smallest currency unit (cents) and cast via Fleetbase\Casts\Money.
+ */
 class TransactionItem extends Model
 {
     use HasUuid;
+    use HasPublicId;
+    use HasApiModelBehavior;
     use HasMetaAttributes;
+    use SoftDeletes;
 
     /**
      * The database table used by the model.
-     *
-     * @var string
      */
     protected $table = 'transaction_items';
 
+    /**
+     * The type of public ID to generate.
+     */
+    protected $publicIdType = 'transaction_item';
+
     /**
      * The attributes that are mass assignable.
-     *
-     * @var array
      */
-    protected $fillable = ['transaction_uuid', 'amount', 'currency', 'details', 'code', 'meta'];
+    protected $fillable = [
+        'public_id',
+        'transaction_uuid',
+        'quantity',
+        'unit_price',
+        'amount',
+        'currency',
+        'tax_rate',
+        'tax_amount',
+        'details',
+        'description',
+        'code',
+        'sort_order',
+        'meta',
+    ];
 
     /**
      * The attributes that should be cast to native types.
-     *
-     * @var array
      */
     protected $casts = [
-        'meta' => Json::class,
+        'amount'     => Money::class,
+        'unit_price' => Money::class,
+        'tax_amount' => Money::class,
+        'quantity'   => 'integer',
+        'tax_rate'   => 'decimal:2',
+        'sort_order' => 'integer',
+        'meta'       => Json::class,
     ];
 
     /**
-     * Dynamic attributes that are appended to object.
-     *
-     * @var array
+     * Dynamic attributes appended to the model's JSON form.
      */
     protected $appends = [];
 
     /**
      * The attributes excluded from the model's JSON form.
-     *
-     * @var array
      */
     protected $hidden = [];
+
+    // =========================================================================
+    // Relationships
+    // =========================================================================
+
+    /**
+     * The transaction this item belongs to.
+     */
+    public function transaction(): BelongsTo
+    {
+        return $this->belongsTo(Transaction::class, 'transaction_uuid', 'uuid');
+    }
+
+    // =========================================================================
+    // Helpers
+    // =========================================================================
+
+    /**
+     * Calculate the line total: quantity * unit_price (in cents).
+     * Returns the stored amount if unit_price is not set.
+     */
+    public function getLineTotal(): int
+    {
+        if ($this->unit_price > 0 && $this->quantity > 0) {
+            return $this->unit_price * $this->quantity;
+        }
+
+        return $this->amount;
+    }
+
+    /**
+     * Calculate the tax amount for this line item based on tax_rate and line total.
+     * Returns the stored tax_amount if tax_rate is not set.
+     */
+    public function calculateTax(): int
+    {
+        if ($this->tax_rate > 0) {
+            return (int) round($this->getLineTotal() * ($this->tax_rate / 100));
+        }
+
+        return $this->tax_amount;
+    }
 }