Hey there, @TaxCatSC. Happy to help out here.

The most common reason that you receive this error is due to cache and cookies in the browser preventing the backend from registering the invite. Your browser stores these files to speed up websites, but over time if not cleared, they can cause issues like this. I recommend telling your employee's to copy the link in the invite email and opening it inside of an incognito or private window in their browser. My colleague has outlined the steps for doing so above.

Once you've done this, keep me updated here. I want to ensure your employees are able to access QuickBooks Online as soon as possible. Have a wonderful Tuesday!