If a contact has already been added to a placement as a timesheet authoriser when a user tries to add them for a second time as a different level of authoriser in the Timesheet Authorisers App, the following error may be triggered:
Errors
Timesheet Authoriser App - SaveTimesheetAuthoriser API Failed - Contact can only be Primary or Secondary
Please remove the existing instance of the contact as an authoriser against the placement, then they can be re-added.