Update projection postition/lastCheckpoint

I’m getting the error: An event emitted in recovery for stream xxx differs from the originally emitted event.
It looks like this can be sorted by updating the projection position/lastcheckpoint via the API, but I can’t get the endpoint /streams/$projections-$projection-checkpoint working.

When I update the position value the position value, the projection gets into a “Starting/LoadStateRequested” state.

Does anybody know the proper way to update the position?