Hello shrummy0001,
Welcome to the Community. I'd be happy to help you get past this error that you're receiving when trying to invite your accountant.
First, I suggest making sure that the accountant's email is in a correct format, and that there aren't any extra spaces, such as the beginning or end. It can also be good to type the email out, instead of copy and pasting it.
Should you continue to receive this error, I recommend clearing the cache in your browser. A browser stores cache to increase loading performance, but can impeded processes. You can locate the steps for supported browsers at the following link: Delete Or Disable Cache And Temporary Internet Files In Your Web Browser..
I'm confident that this information will help to get you back on track.
Please let me know if you have any questions. Wishing you a wonderful start to 2019.
