When you launch Transaction manager it prompts "Install Integration service" as per below image
The issue is caused due to Transaction manager not assigning the appropriate port for the service.
Most of the times the issue is simply fixed by clicking on "Force Session Logoff" and then confirming "Yes"
However, if this doesn't fix the issue you need to follow one of the below procedure to manually assign the Port Number based on the product version. The transaction port number would be provided to you by gotomyerp.
Procedure 1: Manually assign port number if you are using Transaction Manager - SILVERLIGHT INTERFACE
Follow the steps 1, 2, 3, 4, 5 as per the below image and then try to launch Transaction manager again.
Procedure 2: Manually assign port number if you are using Transaction Manager - HTML5 (AKA FOUNDRY)
After you login to the Transaction Manager, click the icon as highlighted in the below image.
Now click on Integration settings
Enter the Integration Service Port number given by gotomyerp, and click "Save"