1. As a KS backer, you have to use the same email address that you are using with Kickstarter.
2. It is unfortunately case-sensitive, so make sure you use capital letters where necessary. This is not an issue for most people, since their email addresses are nearly always in all lower case.
3. MapForge needs internet access for this feature to work, so whitelist the app on Windows Defender (or similar).
I just double-checked, and the MapForge server is currently set to auto-register 3 Add-Ons for you. If you think there should be more, let me know.