Ok so for anyone who has steam. You need to make sure you copy the correct key when you copy text to clipboard. It will not copy the correct one. Just look at your steam keys and just input the Endwalker Collection edition key into the mogstation. You would click on Endwalker registration in the mogstation and then enter the code there and you should be good. It just worked for me.

I feel like a dummy but assumed copy to clipboard was copying the correct key since it was highlighted when copying.