Hey, I weren't able to find a website related section on the forums, so I went for the forum that seemed the most closely linked...
I noticed that when you donate or wait to get a free activation key, it will act normal and give you a Mine-imator key, but then if you press the "Reload this page" button, it seem to generate a new key instead of going back to step one, which I believe can causes problems.
I suggest having that bug fixed as I want others to continue supporting the developers via direct donations or via the other services they chooses to use.
Anyway, have a good day!
~JackShadowFirez