If you encounter this error message, it means that you have inadvertently connected to the source org itself instead of the intended destination org. Follow these steps to resolve the issue:

  1. Revoke OAuth from Source Org:
    • Log in to the source org.
    • Click on the Profile icon and go to Advance User details.
    • In th O Aauth apps section, revoke all the records with Mass File Migrate application.
  2. Log in to the Destination Org:
    • Log in to the intended destination org where you want to migrate files/attachments.
    • Note:  Please keep only the source and the destination org logged in to the browser. 
  3. Retry Connecting:
    • Once logged in to the destination org, attempt to connect the Mass File Migrate app from source org again.
    • Follow the standard connection process to authorize access to the destination org.

By following these steps, you should be able to resolve the error and establish the correct connection between the Mass File Migrate app and the destination org for seamless file/attachment migration.