Does anyone know why this appears on my registration page?

A license for the following products can be registered on this page:

FINAL FANTASY XIV: Stormblood Standard Edition Steam / Mac
FINAL FANTASY XIV: Stormblood Collector's Edition Steam / Mac
FINAL FANTASY XIV Online Complete Edition Steam / Mac
FINAL FANTASY XIV Online Complete Collector's Edition Steam / Mac

I am trying to register my code for the PC version of Stormblood on the mogstation, and I've noticed that there's a giant purple button which says "Enter Expansion Registration Code", which takes me to that warning. I don't have a MAC, and after a weekend of early launch horrors, I don't want to register a wrong version and find myself locked out of the game. Has anyone else experienced this? Btw my version is from steam.