authError when loging in to second account

[Di-Mon]

I've set up script and keys with Google Cloud as described.
The app successfully launched, I've managed to login to account and script found 365 subscriptions. Though when I try to login to second account which I want transfer subscribtions to, the auth window open, I logging in in it, but after it is closed in main window I am getting authError

cb=gapi.loaded_0?le=scs:226 GET https://content-youtube.googleapis.com/youtube/v3/subscriptions?order=alphabetical&part=snippet&mine=true&maxResults=50&key=AIzaSyCgJVEo4KllGvzGJ_e8lP0oG_GUWLVhoec 401 vh @ cb=gapi.loaded_0?le=scs:226 h @ cb=gapi.loaded_0?le=scs:226 wh @ cb=gapi.loaded_0?le=scs:227 (anonymous) @ cb=gapi.loaded_0?le=scs:227 d @ cb=gapi.loaded_0?le=scs:166 b @ cb=gapi.loaded_0?le=scs:161

the api is set up in "Testing" mode with both emails from first and second accounts whitelisted.