diff --git a/app/Domains/Purchase/Exceptions/InsufficientStockException.php b/app/Domains/Purchase/Exceptions/InsufficientStockException.php
new file mode 100644
index 0000000..62f7787
--- /dev/null
+++ b/app/Domains/Purchase/Exceptions/InsufficientStockException.php
@@ -0,0 +1,36 @@
+<?php
+
+namespace App\Domains\Purchase\Exceptions;
+
+use RuntimeException;
+
+class InsufficientStockException extends RuntimeException
+{
+    /**
+     * @param  array<int, array{
+     *     index: int,
+     *     catalog_item_id: int,
+     *     variant_id: int|null,
+     *     requested_quantity: int,
+     *     available_quantity: int,
+     *     message: string
+     * }>  $unavailableItems
+     */
+    public function __construct(
+        public readonly array $unavailableItems,
+    ) {
+        parent::__construct(
+            collect($unavailableItems)->pluck('message')->unique()->implode(' '),
+        );
+    }
+
+    /** @return array<string, array<int, string>> */
+    public function errors(): array
+    {
+        return collect($this->unavailableItems)
+            ->mapWithKeys(fn (array $item): array => [
+                "direct_items.{$item['index']}.cantidad" => [$item['message']],
+            ])
+            ->all();
+    }
+}
diff --git a/app/Domains/Purchase/Services/Checkout/StartCheckoutService.php b/app/Domains/Purchase/Services/Checkout/StartCheckoutService.php
index 152dadf..6c3c7a3 100644
--- a/app/Domains/Purchase/Services/Checkout/StartCheckoutService.php
+++ b/app/Domains/Purchase/Services/Checkout/StartCheckoutService.php
@@ -8,6 +8,7 @@ use App\Domains\Catalog\Models\CatalogItem;
 use App\Domains\Catalog\Models\Variant;
 use App\Domains\Catalog\Services\CatalogInventoryService;
 use App\Domains\Purchase\Models\Purchase;
+use App\Domains\Purchase\Exceptions\InsufficientStockException;
 use App\Domains\Purchase\Services\UserPurchaseLimitService;
 use App\Domains\Tenant\Models\Tenant;
 use Illuminate\Support\Collection;
@@ -70,6 +71,7 @@ class StartCheckoutService
         $lines = collect(array_values($directItems))
             ->map(function (array $item, int $index): array {
                 return [
+                    'index' => $index,
                     'catalog_item_id' => (int) $item['catalog_item_id'],
                     'variant_id' => isset($item['variant_id']) ? (int) $item['variant_id'] : null,
                     'quantity' => (int) $item['cantidad'],
@@ -124,30 +126,32 @@ class StartCheckoutService
                 );
             });
 
+        $unavailableItems = $resolvedLines
+            ->map(function (array $line): ?array {
+                $availableQuantity = $this->inventory->availableQuantity($line['selection']);
+
+                if ($availableQuantity === null || $availableQuantity >= $line['quantity']) {
+                    return null;
+                }
+
+                return $this->unavailableItem($line, $availableQuantity);
+            })
+            ->filter()
+            ->values()
+            ->all();
+
+        if ($unavailableItems !== []) {
+            throw new InsufficientStockException($unavailableItems);
+        }
+
         foreach ($resolvedLines as $line) {
-            $availableQuantity = $this->inventory->availableQuantity($line['selection']);
-
-            if ($availableQuantity !== null && $availableQuantity < $line['quantity']) {
-                throw ValidationException::withMessages([
-                    "{$line['field']}.cantidad" => $this->stockMessages->build(
-                        $line['catalog_item'],
-                        $line['selection'],
-                        $availableQuantity,
-                    ),
-                ]);
-            }
-
             try {
                 $this->inventory->reserve($line['selection'], $line['quantity']);
             } catch (\InvalidArgumentException) {
                 $availableQuantity = $this->inventory->availableQuantity($line['selection']) ?? 0;
 
-                throw ValidationException::withMessages([
-                    "{$line['field']}.cantidad" => $this->stockMessages->build(
-                        $line['catalog_item'],
-                        $line['selection'],
-                        $availableQuantity,
-                    ),
+                throw new InsufficientStockException([
+                    $this->unavailableItem($line, $availableQuantity),
                 ]);
             }
         }
@@ -176,6 +180,33 @@ class StartCheckoutService
         return $this->loadPurchase($purchase);
     }
 
+    /**
+     * @param  array<string, mixed>  $line
+     * @return array{
+     *     index: int,
+     *     catalog_item_id: int,
+     *     variant_id: int|null,
+     *     requested_quantity: int,
+     *     available_quantity: int,
+     *     message: string
+     * }
+     */
+    private function unavailableItem(array $line, int $availableQuantity): array
+    {
+        return [
+            'index' => $line['index'],
+            'catalog_item_id' => $line['catalog_item_id'],
+            'variant_id' => $line['variant_id'],
+            'requested_quantity' => $line['quantity'],
+            'available_quantity' => $availableQuantity,
+            'message' => $this->stockMessages->build(
+                $line['catalog_item'],
+                $line['selection'],
+                $availableQuantity,
+            ),
+        ];
+    }
+
     /** @param array<string, mixed> $purchaseData */
     private function startFromCart(
         Tenant $tenant,
diff --git a/bootstrap/app.php b/bootstrap/app.php
index 3e6b9b1..8a1b5e6 100644
--- a/bootstrap/app.php
+++ b/bootstrap/app.php
@@ -2,6 +2,7 @@
 
 use App\Domains\Auth\Exceptions\AccountLockedException;
 use App\Domains\Ticket\Exceptions\TicketNotAvailableException;
+use App\Domains\Purchase\Exceptions\InsufficientStockException;
 use App\Http\Middleware\EnsureAdminAppTenant;
 use App\Http\Middleware\EnsureScannerTenant;
 use App\Http\Middleware\EnsureTenantHasMenu;
@@ -74,6 +75,18 @@ return Application::configure(basePath: dirname(__DIR__))
                 'message' => __('api.errors.forbidden'),
             ], 403);
         });
+        $exceptions->render(function (InsufficientStockException $exception, Request $request) {
+            if (! $request->is('api/*')) {
+                return null;
+            }
+
+            return response()->json([
+                'code' => 'purchase.insufficient_stock',
+                'message' => $exception->getMessage(),
+                'errors' => $exception->errors(),
+                'unavailable_items' => $exception->unavailableItems,
+            ], 422);
+        });
         $exceptions->render(function (ModelNotFoundException $exception, Request $request) {
             if (! $request->is('api/*')) {
                 return null;