Google Authenticator on Apple devices, certain secrets are not valid

Question

We\'ve incorporated two factor authentication into one of our applications using Google Authenticator. In QA, something really weird turned up. While I managed to fix it,

Answer 1

5 years later... We can only get Google Authenticator to accept secret keys that are 16 digits long. Shorter and longer keys just fail with "Invalid barcode. The barcode ... is not a valid authentication token barcode." Lost a lot of time troubleshooting this, hope it helps.