‘level’ GET parameter not taken into account on [pmpro_checkout] page

This seems to be an exact replica of https://www.ads-software.com/support/topic/level-post-not-taken-into-account-on-pmpro_checkout-page/

We are using the “Post name” option for Permalink structure. Setting it to “Plain” results in the correct behaviour being observed.

Sadly, the patch provided on the original topic doesn’t appear to be working. ??

The page I need help with: [log in to see the link]