How can I fix Gmail account info errors in my Mail app?

hey all so yesterday morning i woke up and the mail app said account info wrong turned app off and on went then getting email was really slow took time and only works fast on charge ive woke up today with the same error and my email number notification has increased but no new email this is really annoying had things with connection problems before but this is the worst and it’ll just sit there after the error gone saying connecting

[Edited by Moderator]

Original Title: mail app not working with gmail