When making a new assignment in the GMC, some DPAs/DSAs will come across the following message:
"Assignment not created - the assignment already exists"
DPAs/DSAs will get this message when trying to give an assignment to a user when it already exists in the GMC, either assigned or unassigned.
In most cases, it will most likely be unassigned, which was why it was not readily apparent that the user already had the assignment.
To "reassign" the role, DPAs/DSAs should go to Manage Assignments.
When in Manage Assignments, search for the user, the role and make sure that "Unassigned" is selected from the appropriate drop down.
After clicking "search", it should show any unassigned roles that exist for that user in the GMC.
Simply click "reassign" next to the assignment and it will sync back into Gateway.