We found this post: «Paid Membership» plugin with PayPal integration! (version 3.0, 2015-08-31) Guess that will be ok as well since we can redirect users on WP to register on Discourse and use SSO plugin so users can log into both sites.
However, there seems to be a bit of bickering going on between the developer and some users. So not sure if he can be trusted on what kind of good/bad support he really does provide?