I'm failing to verify itunes

If you can’t receive a verification code on your trusted devices automatically, you can get one from Settings, even if your device is offline.

From your iPhone, iPad, or iPod touch

If your device is online:

1. Go to Settings > [your name].
2. Tap Password & Security > Get Verification Code.

If your device is offline:

1. Go to Settings > [your name].
2. Tap Password & Security. 
3. A message says "Account Details Unavailable." Tap Get Verification Code.

Please see the article below.

Get a verification code and sign in with two-factor authentication - Apple Support

Hope this helps.