Cannot add removed mail account on iMac

I deleted mail account from MAC after update and changing my password bc could not retrieve mail.

I then went to add Gmail account back through mail/acounts. It accepted my credentials and then a 400 error popped up" the server cannot process the request bc it is malformed. It should not be retried". On my iPhone and iPad it accepted my credentials and mail functions properly. All devices are synced, have been shut down and restarted multiple times. However MAC continues with same error .

Any thoughts?

[Re-Titled by Moderator]