Can't get checkbox or radio buttons to sync

I have a yes/no question set up in MailChimp as a List Field of the radio button type (“List Fields and *|MERGE|* Tags” page). I would prefer a checkbox, but I don’t see that option. Anyway, no matter what fields I try to create in CIMY, I cannot get them to sync with MailChimp (I’m using AutoChimp for syncing). Text fields work fine.

I have a radio button in MailChimp with a Field Label of “Related email?”, options “Yes” and “No”, Merge Tag “RELATED”. I then create an Extra Field in CIMY with the type “radio”, name “RELATED”, Value “Yes”, and Label “Yes”. Finally I create another Extra Field in CIMY with the type “radio”, name “RELATED”, Value “No”, and Label “No”. The AutoChimp fields RELATED are assigned to the MailChimp field “Related email?” in AutoChimp > Mailing Lists.

What am I missing?

https://www.ads-software.com/extend/plugins/cimy-user-extra-fields/