Hi robyno8888,
This issue commonly arises when the email address isn't associated with their my.MYOB account. To resolve this, navigate to Setup >> User Access and choose the desired User ID. Next, opt for 'This user will sign-on with a my.MYOB account (Recommended)' and input their email address in the Email field. Afterward, save the changes. This action links the User ID with the specified email address, allowing the client to successfully access the MYOB Invoices app.
If you're still having issues after following the steps above, you can contact our support team for more help. The best ways to contact our support team are through live chat (via our virtual assistant MOCA) or by raising a support ticket through myaccount.myob.com.
Regards,
Earl