If you are having issues logging into your COD or Warzone account and see the registration Error 0. Follow these 5 steps in this video and it should fix the problem.
A Registration error will occur if you attempt to register for an account in game using an email address that is already tied to an existing Activision / Call of Duty account.
So, to get around this issue you need to follow the following steps.
Step 1
Close you game and do a hard reset on your console or restart your PC. (hold the power button for 10 seconds on Xbox)
Step 2
Try and login again using your Activision email and password. If this doesn’t work on your web browser go and login via your network (PSN / XBOX / STEAM) or email and password.
Step 3
Make sure the account you want to use (XBOX / PSN / STEAM) is linked up to your Activision account.
Step 4
Once you have linked your account try and login again after restarting your console or PC.
Step 5
If this still doesn’t work, try resetting your password using the link below. Follow the on-screen instructions and once this has been done try and login again with new password.
Hope this has helped you and as always leave any questions below in the comments.