how do i add co-hosts to a recurring meeting schedule??

Welcome to the Zoom Community, @aec-ewc.

Co-Hosts aren't added prior to a meeting... they're only added by the Host inside the meeting.

You might be thinking of an Alt-Host, which becomes a Co-Host once they're in the meeting -- if there is already a host, otherwise, they become the Host.  Note that Alt-Hosts must meet both of the following criteria:

1. Must be a Licensed (paid) account.
2. Must be on the same Owner's account as the grantee.  In other words, you both must be on the same organizational account.

Where are you supposedly adding co-hosts that it is not accepting?  I'm guessing it was the Alt-Host section.