In an effort to try and bring both individual product subscriptions as well as a discount membership, it was overlooked that the two apps might not necessarily want to play happily together. Not my fault! I blame the the modrons!
It took some hours in chats with tech support to finally figure it out. It seems that things should be working properly now!
You might have also noticed the site looks shiny and new! This update was a long time coming, and running into issues with the apps I was trying to use pushed me into finally finishing it. There's gonna be some small appearance tweaks happening over the next few months probably, so that I get things looking just how I want.