How to check if a person is in a group?

Question

API

Is it necessary to have an application to check if a person is a subscriber of the group where the bot works?
If not, how can this be implemented? (You will need to display a message if the person is not subscribed.

spoiler

switch ($data->type){

    case 'confirmation':
        echo $confirmation_token;
        break;
    case 'message_new':
        $user_id = $data->object->user_id;
        $sostoit = file_get_contents('https://api.vk.com/method/groups.isMember?group_id='. $group_id .'&user_id='. $user_id .'extended=1');
        $member = json_decode($sostoit, true);
        if ($member['response']['member']==0){
          $request_params = [
            'message' => "Сначала в группу вступи!",
            'user_id' => $user_id,
            'access_token' => $token,
            'v' => $api_version
          ];
          $get_params = http_build_query($request_params);
          file_get_contents('https://api.vk.com/method/'. $msg_send . $get_params);
          echo('ok');
          break;
        }
          else { 
                          Тут остальной код, если человек состоит в группе
}

In unsuccessful requests writes

Error: HTTP response code said error. Attempt 1/5
Error: HTTP response code said error. Attempt 2/5

Okay with the first mistake, but with the second. Is it necessary to have an application? And how in general to connect it to the bot and take data from there?

Answer 1

Issue resolved.
The group membership check request should look like this:
https://api.vk.com/method/groups.isMember?group_id= ".$group_id ."&user_id=".$user_id."&extended=1&access_token=".$token ."&v=".$api_version);