用于属性验证的消息，作为laravel中的数组返回

I am using the messages method to return the error messages for each of my attributes .. it happens that for each attribute it returns an array and I would like it to return a string.

In my model...

public function validate()
{
    $validator = Validator::make($this->attributesToArray(), $this->validationRules);

    if($validator->fails()) {
        throw new \App\Exceptions\OperationNotAllowed('validation failed', $validator->messages(), '422');
    }

    return true;
}

In my Exception

public function render($request)
{
    return response()->json([
        'error'   => $this->erro,
        'details' => $this->details,
    ], $this->code);
}

Look how the result is coming out

And I wish that instead of array for each attribute the error message would be a string