I just set up two-factor authentication on Amazon, choosing "Authenticator App" (instead of text code). Using 1Password for iPhone I tapped the QR code icon to enter the code into the newly-created "One-Time Password" field I had just created. Though everything seems to work as it should, as soon as the login process stops I'm on a plain-vanilla page in Amazon (not yet logged in). I tried this several times with the same result. I've attached a screenshot (no sensitive information on it).
1Password Version: 7.3.1
Extension Version: Not Provided
OS Version: iOS 12.3
Sync Type: AgileBits