fix(purchase): unify expired checkout errors

lang/en/api.php

@@ -36,6 +36,7 @@ return [
         'variant_required' => 'You must select a variant for this item.',
     ],
     'purchase' => [
+        'expired' => 'The purchase has expired. Please start a new purchase.',
         'variant_change_disabled' => 'Variant changes are disabled for this purchase.',
         'source_required' => 'A cart or direct item is required.',
         'payment_method_required' => 'The purchase payment method must be selected before finalizing.',

lang/es/api.php

@@ -36,6 +36,7 @@ return [
         'variant_required' => 'Debe seleccionar una variante para este ítem.',
     ],
     'purchase' => [
+        'expired' => "La compra venci\u{00F3}. Inici\u{00E1} una nueva compra.",
         'variant_change_disabled' => 'El cambio de variante está deshabilitado para esta compra.',
         'source_required' => 'Se requiere un carrito o un producto directo.',
         'payment_method_required' => 'Debes seleccionar el método de pago antes de finalizar la compra.',