Why doesn't Domain-wide Delegation work in Google Cloud Gmail API?

Question

PHP

In the gmail settings there is such an opportunity to forward all letters to another mail

. There was a need to implement this through the gmail api. The application has been in the google cloud for a long time, added the use of gmail api, a service account, tied it all to the desired domain, then created an account in google workspace, added the application, domain there, confirmed the domain. But still, the status of the service account has not changed in the google cloud

The script reads the necessary data (auto_forwarding), but when you try to change it, it returns an

error developing for personal use.