I am trying to buy an add-on for my Plesk license in Plesk Online Store and get the error message below:
Selected feature is not compatible with your license – like if you are buying Plesk 12 feature for Plesk 11 license.
Error message indicates that the license key version provided during order placement is not compatible with the chosen add-on.
If you have a Plesk 11 or older Lease license that was purchased from a Plesk reseller/partner or Plesk 11 and below Retail (one-time purchase) license, please contact one of Plesk resellers and check with them if they offer required add-on.
Please check this article for more details on compatibility of Plesk licenses and add-ons: KB #123993