Make sure to use the correct login credentials of the subscribed account. Also, update the app to its latest version.
If the credentials used are correct, and you're still receiving the same error, I recommend contacting our QuickBooks Self-Employed support. We will be able to check your account and see what's causing this. You can send us an email here: https://help.quickbooks.intuit.com/en_US/contact?product=qbse. Fill out the necessary information, and click Ask Your Question.
Don't hesitate to leave a comment below if there's anything else I can help you with.