Registering code confusion

Does anyone know why this appears on my registration page?

Quote:

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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

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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.

Do you have the Steam version of ARR? If yes, then the expansion packs also have to be from Steam.