Вы можете вручную l oop над ошибкой MessageBag и построить ответ для замены ключа
$validator = Validator::make($request->all(), [
'first_name' => 'required',
'last_name' => 'required',
'email' => 'required|email|unique:users',
'fcm_token' => 'required',
'password' => 'required',
'c_password' => 'required|same:password'
]);
$errors = [];
foreach ($validator->errors()->messages() as $key => $value) {
if($key == 'email')
$key = 'message';
$errors[$key] = is_array($value) ? implode(',', $value) : $value;
//implode is for when you have multiple errors for a same key
//like email should valid as well as unique
}
$result = array("status" => count($errors)?0:1, 'data'=>$errors);
return $result;