I am having a similar problem.  Yesterday 4/28/21, I tried added a new employee as a time tracker.  He received the email invitation to set up his log in credentials and set them up.  After doing that he tried to log in to QBO but keeps getting an error message - "There's a problem on our end, but we're on it."

I have tried deleting him and re-adding him several times to no avail.

I have tried deleting him as an employee and user and then re-adding as an employer and then a user several times to no avail.

The new employee has cleared cache and tried different browsers and he continues to get the same error message.

Yesterday I was passed to 4 different customer service people at Intuit by phone with wait/hold times from 30 to 60 minutes and no one could tell me how to fix this so my new employee can track his time.

Any other ideas on how to get this working?????????