If you go to connect Transaction Pro Importer to your client's company file and get the error:

Error Code: app_already_purchased

Message: The application has already been subscribed to by another user for this company. Please contact (email address) to make changes to this subscription.

If this is a current App please ask the person listed in the error message to add you as a user for the App.If you no longer wish that this person be the Admin of the App if they are still a current QuickBooks Online user for that company ask this person to sign into QuickBooks Online go to Apps/My Apps and then look for the App in question and select the disconnect link.
If this person is no longer part of this QuickBooks Online company file the fastest way to get this resolved is to contact the App developer with the QuickBooks Online company id and ask that the Admin user be changed.

(From the Transaction Pro Support Article)

Learn more about Transaction Pro Importer.

Updated: April2017