Why does sometimes 2FAS Auth send tokens automatically and sometimes asks to select a token?

Exchanging information between the browser and 2FAS Auth on your phone is similar to speed dialling. If we want to call John, we don’t enter his phone number because remembering it doesn’t make sense. When we met him for the first time, we entered his mobile number and assigned him the name John in the phone book. Later, it is enough to choose a contact named John and call.

It is similar when the browser asks for the code for Twitter.com, for example. It sends a request to 2FAS Auth, which asks you to select a code/token, because it doesn’t know which token should be assigned to the X.com domain. That’s why the first time, we need to bind the domain with the token. The next time you log in, the browser will ask for a code for X.com, and you will get an answer with the correct token/code immediately.