The way this works is that the Code-Based Linking allows Fire TV Stick users can sign in without the need of entering Amazon credentials with the on-screen keyboard using the Fire TV remote. On the setup page, you will see a URL that could be opened on the web browser on a smartphone or tablet.
The Amazon Fire TV Stick family of media players are perhaps the slickest way of upgrading your smart TV experience with access to video streaming platforms including Amazon Prime Video, Netflix, Disney+ Hotstar, Voot, Zee5, Sony Liv, Lionsgate Play, Discovery+ and more. However, there was one really annoying thing, and that is when you set up the Fire TV Stick for the first time, you had to manually enter your Amazon credentials, that is your ID and password, using the remote and the on-screen keyboard. Chances are, your Amazon ID would be your email ID, which would be quite long as it is. Now, Amazon says you can use an authentication code instead to set this up.