Bought on sxflashcards.com too. Had also needed the support chat for the paypal payment. After I told that I sent the money, I instantly got the key via the same chat. Really good and fast experience overall.
Edit: I also had to use a random address, because I'm from outside US. Was no problem...
If you're not connected to WiFi, then the cart will just update to 3.0.1. Unfortunately the exploit just works till 3.0.0...
Without updating I don't think there will be a way to play this game (even after homebrew/piracy in 3.0.0)
My Switch was never on WiFi. It was on 3.0.0. Cart updated to 3.0.1. There is no more hope, sry.
Correction: It was on WiFi to update to 3.0.0. Never again since then.
I got a Switch on 3.0.0, Mario will arrive later. If no one posts until then, I will gladly confirm it. (I don't expect it to be something else, because then someone would have posted something here (maybe))