The Affiliates manager plugin can be integrated with the S2Member plugin so you can reward affiliates for sending members.
Step 1 (Install the Integration Addon Plugin)
Download and Install the S2Member Integration addon.
Step 2 (Keep the Main Plugins Active)
Simply keep the Affiliates Manager and the S2Member plugins active in your WordPress site.
The affiliate plugin will track all the referrals and give commission accordingly if a referred user pays for a membership.