How to receive emails from Gmail API through a service account?

Question

Google

Logged into the Google Api console
Enabled the Gmail API
Created a service account
Downloaded the access file
Wrote a script strictly according to the instructions (according to this instruction, Google Spreadsheets Api works for me through the service account)
I call the Gmail Api method...
For some reason I get 400 Bad Request
Could it be that letters from a specific person cannot be received through a service account, but is it necessary to do tokenization with oauth2?
Otherwise, it is not clear to me why 400 Bad Request, since the official release lib is used.

Answer 1

gmyl works fine via IMAP, if that