Authenticator “Set up account” doesn’t exist

I went to set up the alternative second step with the Authenticator app on iPhone. But when I get to where it says to tap on “Set up account” within the app, the option does not exist to set up an account. I have just the one other account I had set up for another website, but no option to add another account. Is the Authenticator app only able to work with a single website? Or is it just no longer useful for purposes of this plugin?