Sorry, you’ve lost me 
You seem to be saying here that users have a licence on Wordpress and you want their access to Discourse to be dependent on it.
You seem to be saying here that the “licence” you were referring to above is a product you’re selling through Easy Digital Downloads? If this is the case this is not about webhooks.
I think you need to hire someone to help you with the specific setup you’ve got going there as you’ve gone beyond the WP Discourse plugin here. You can describe your usecase in marketplace and you’ll get some folks who can help you out.