I’m sure you’ve probably contributed before and the extra step, the conversion, takes a minute or two with Vanguard. Buy the website doesn’t know if you meet all of the conditions. Only you or your advisor knows that.
The main risk to conversion when I do them is I accidentally add a zero and convert $60k instead of $6k. But when you do a backdoor, the post tax money you contributed should be the only money you have in the tIRA. So there would be no way to make the extra zero mistake.