diff --git a/services/nginx/app/classes/subuser_permission_templates_service.php b/services/nginx/app/classes/subuser_permission_templates_service.php
index 6abbe49d..12a84ff2 100644
--- a/services/nginx/app/classes/subuser_permission_templates_service.php
+++ b/services/nginx/app/classes/subuser_permission_templates_service.php
@@ -178,6 +178,23 @@ class subuser_permission_templates_service
         ];
     }
 
+    /**
+     * @return array{enabled:bool,permissions:array<int,string>}|null
+     */
+    public function expandTemplateForWritePayload(?string $templateKey): ?array
+    {
+        $key = $this->normalizeTemplateKey($templateKey);
+        if ($key === self::TEMPLATE_CUSTOM) {
+            return null;
+        }
+
+        if ($key === null) {
+            throw new \InvalidArgumentException('Unknown driver access template.');
+        }
+
+        return $this->expandTemplate($key);
+    }
+
     public function normalizeTemplateKey(?string $templateKey): ?string
     {
         if ($templateKey === null) {
diff --git a/services/nginx/app/routes/subusersRoute.php b/services/nginx/app/routes/subusersRoute.php
index 651915f2..65c723c2 100644
--- a/services/nginx/app/routes/subusersRoute.php
+++ b/services/nginx/app/routes/subusersRoute.php
@@ -140,7 +140,7 @@ class subusersRoute
 
         $templateKey = (string)self::getParameter('permission_template_key');
         try {
-            return (new subuser_permission_templates_service())->expandTemplate($templateKey);
+            return (new subuser_permission_templates_service())->expandTemplateForWritePayload($templateKey);
         } catch (\InvalidArgumentException $exception) {
             $response->error($exception->getMessage(), 400);
         }
diff --git a/services/nginx/app/tests/Unit/Subusers/SubuserPermissionTemplatesTest.php b/services/nginx/app/tests/Unit/Subusers/SubuserPermissionTemplatesTest.php
index e04960ce..4945c7f7 100644
--- a/services/nginx/app/tests/Unit/Subusers/SubuserPermissionTemplatesTest.php
+++ b/services/nginx/app/tests/Unit/Subusers/SubuserPermissionTemplatesTest.php
@@ -44,3 +44,25 @@ it('expands and classifies practical driver access templates', function (): void
         ->and($service->classify(['VEHICLES_LIST'], true))
         ->toBe(subuser_permission_templates_service::TEMPLATE_CUSTOM);
 });
+
+it('treats custom as a raw permissions marker in write payloads', function (): void {
+    $service = new subuser_permission_templates_service();
+    $driver = $service->expandTemplateForWritePayload(subuser_permission_templates_service::TEMPLATE_DRIVER);
+
+    expect($service->expandTemplateForWritePayload(subuser_permission_templates_service::TEMPLATE_CUSTOM))
+        ->toBeNull()
+        ->and($driver['enabled'])
+        ->toBeTrue()
+        ->and($driver['permissions'])
+        ->toBe([
+            'VEHICLES_LIST',
+            'SELFSERVE_LIST',
+            'SELFSERVE_ADD',
+            'BOOKINGS_LIST',
+            'BOOKINGS_ADD',
+            'ORDERS_LIST',
+        ]);
+
+    expect(fn () => $service->expandTemplateForWritePayload('missing-template'))
+        ->toThrow(\InvalidArgumentException::class, 'Unknown driver access template.');
+});
diff --git a/services/nginx/app/tests/Unit/Subusers/SubusersRouteManagementContractTest.php b/services/nginx/app/tests/Unit/Subusers/SubusersRouteManagementContractTest.php
index faa3fde1..fd4801ca 100644
--- a/services/nginx/app/tests/Unit/Subusers/SubusersRouteManagementContractTest.php
+++ b/services/nginx/app/tests/Unit/Subusers/SubusersRouteManagementContractTest.php
@@ -70,6 +70,16 @@ it('links grant disable operations to SUBUSERS_DELETE for own-customer managers'
     expect($normalized)->toContain("requireManagedCustomerScope(subusers_permission_node_key::SUBUSERS_DELETE, \$targetCustomer);");
 });
 
+it('parses custom grant writes through raw permissions instead of template expansion', function (): void {
+    $routeFile = app_path('routes/subusersRoute.php');
+    expect(is_file($routeFile))->toBeTrue();
+
+    $code = (string)file_get_contents($routeFile);
+    $normalized = preg_replace('/\s+/', ' ', $code);
+
+    expect($normalized)->toContain('expandTemplateForWritePayload($templateKey)');
+});
+
 it('prevents own-customer managers from editing driver-owned account profiles', function (): void {
     $routeFile = app_path('routes/subusersRoute.php');
     expect(is_file($routeFile))->toBeTrue();