Adding new episode credit to existing one for series - Declined Reason Badly Formatted

So one credit exists already as cast in one episode and another needs to be added so I went into the new episode and edited that episode to add a new credit for the same actor and character but the response was "Reason Badly Formatted. Your contribution has been declined.Your contribution did not meet our formatting standards. Please review our submission guides. I feel (I maybe wrong) they want me to edit the original credit instead but I have spent hours looking and reading guidelines and can't find how to add the 2nd episode - if i try and edit the original credit it just lets me change the basic info but there is no episode box to add the additional episode as the orginal credit was added at episode level