If you recieved email about waiting for 48 hours for Apple ID….
I got the email on Tuesday mid day saying the email I entered wasn’t linked to an Apple ID account, I resubmitted my email and didn’t hear back anything. I did however go into the wallet app and click the plus button to add new card a few minutes ago and boom there it was, it let me sign up for the Apple Card. I saw a YouTuber saying he did it this way and it worked so I figured I would give it a shot. I tried a few times already but it finally just popped up as an option for me and now I have the Apple Card in my wallet. Hope this helps someone who’s trying to get it! If it doesn’t show up as an option try again every few hours or next day.