How to get your subscriptions through the YouTube API without nerves?

Question

YouTube

I created a new YouTube account for testing purposes. I am getting accessToken for this account and trying to get my subscriptions via YouTube Api. I am using Google APIs Client Library for PHP..

$data = $service->subscriptions->listSubscriptions('snippet', ['mine' => 'true']);

I get the error:
"domain": "youtube.subscription", "reason": "subscriberNotFound", "message": "The subscriber identified with the request cannot be found.", "locationType": "parameter", "location": "channelId" "code": 404, "message": "The subscriber identified with the request cannot be found."
Then I changed the account to my old one, got an accessToken for it and got a successful result.
But why is an error being thrown on a new account?