Membership add-on not available for Affiliates

Hi,
The membership add-on for the Affiliates plugin is not available.
It says "Membership -- plugin not installed", under Add-ons.
When visiting plugin section I can clearly see Membership v3.4.4.1 activated, so it is installed.
What am I missing?

If you wonder: Another programmer did the implementation of Membership so this account of mine only has Affiliates in bought history