For creating a paid membership, I installed the plugin Memberful on my wp-site, that offers Discourse integration. The payment works in test mode, but the users are not added to Discourse.
Could these settings be the problem? I am not sure whether they are overridden by Memberful or I set them prior to using Memberful:
SSO is enabled, but there is still turned on: 1. Invite only 2. login required
and 3. ‘allow new registrations’ is disabled.
Have you gone through the steps for setting up SSO that are outlined at the top of the SSO Provider tab on WordPress?
The way SSO (Single Sign On) works is that it doesn’t create the user on Discourse until they login to Discourse from WordPress. The easiest way to test if it’s working is to first try logging into Discourse yourself with SSO enabled. If that works, create a test user on your WordPress site with a throwaway email address. Try logging into Discourse as that user. Discourse should automatically create a user.