Making group joins automatic to an external pricing plan

I couldn’t see that one on https://www.wix.com/app-market - could you provide us with a link?

You’re going to need to point us at what you’re using and any documentation if you want us to help you figure this out.

Is the content being sold on your Wix site, or is the plan for it to only be available through your Discourse instance? if the latter have you looked at this?