If the user cannot log in with that confirmation key, consider the following:
  1. These codes are one-time use only so they can't be reused.
  2. Any spaces before or after the code can make it invalid. If the user is copy and pasting the code he/she will want to make sure there aren't any spaces being copied with the code.
  3. The user needs to make sure they enter the confirmation code right away or the code may time out.