Setting up Android-based app verification
Before you start any of this, go ahead and download the official Android or iOS Twitter app. Third party apps will not do you any good when it comes to Twitter verification.
My primary phone is an Android phone, so I'm only able to go all the way with the Android version of the app for verification. That's because Twitter requires a real phone number prior to setting up verification. For the iOS side, I'll get you to the right screens, but it wouldn't hurt for you iOS users to read this section just to see it all the way through.
The first thing you may find when logging in with your Android app is the requirement that you enter a verification code. Since I use text-message based verification, when I opened my Twitter app, I was presented with this screen. Shortly after, I got a text on my phone and had to switch to the message app, get the code, switch back here, and enter it.
To get started, click the three-dot icon on the upper right of your Android screen and then select settings from the drop-down menu.
Now, select the account you want to verify. In my case, it's @DavidGewirtz. Yours will, of course, be your account. You might also notice the option to add an account.
I tried this, thinking I could use this approach to verify a second account, but oddly enough, as soon as you get into the settings and select Security, you're told you need a unique phone number. No joy that way!
In any case, once you tap your user name, you'll be presented with the Settings screen. Scroll all the way down to the bottom, and you'll see Security. Tap that.
Next, the Login verification screen will come up. Click the radio box.
First comes a warning. Tap OK.
Finally, you'll be asked if you want to save your backup code. I would write it down, but I don't like the idea of saving it in my gallery.