mail app keeps prompting for password on an O365 mail account

I have a user that the mail app stops working almost every day and gets prompted for his password. We go into settings|Mail|accounts. Then under account is says "Re-enter password" but without even pressing the re-enter password it disappears and his e-mail starts flowing again. This is an O365 mail account. He's using SE3 iPhone and his IOS version is 17.4. I have tried swapping out the iPhone and the new one does the same thing. Any help would be greatly appreciated.