The "Code was already redeemed" error message is coming from google authentication and not related to CPM's PIN system.

Try the following:

  • Make sure you are using a supported browser such as Chrome, Safari, or Firefox.
  • Clear your cache.  
  • Make sure you are not using parental control software or adblocker, which can disrupt network communications.

You could also try logging on to a different device which usually solves the situation.