laravel api validation custom message

I am trying to write a custom message for a validation in laravel. I have checked online and I saw some post where others solve that same issue by adding a protected function. I have also added the function to my code but it is not working. This is my code This is myFormController.php:

public function req(RegistrationRequest $request){ $validated = $request->validated(); return $validated; )}

This is the RegistrationRequest.php:

use Illuminate\Contracts\Validation\Validator; use Illuminate\Http\Exceptions\HttpResponseException;

public function authorize() { return true; }

public function rules()
{
    return [
        'email' => 'required|email',
        'firstname' => 'required|string|max:20',
        'lastname' => 'required|string|max:50',
        'password' => 'required|min:8',
    ];
}  protected function failedValidation(Validator $validator) {
throw new HttpResponseException(response()->json($validator->errors(), 422)); }

When that did not work, I used this:

protected function failedValidation(\Illuminate\Contracts\Validation\Validator $validator) { throw new \Illuminate\Validation\ValidationException(response()->json($validator->errors(), 422)); }

Please what am I doing wrongly?

via Chebli Mohamed