Are you using the same email address that was used when SF initially registered? Was SF activated prior? .. more than one PC? Was SF purchased from a third-party seller?
btw, welcome to the Magix Sound Forge users community @Berklas.
I do not remember to activate it, and if so, I am sure I must have used one of my 3 emails I am using all the time, but none of them seems to be linked to the registration. I bought it as bunle on HumbleBudle website and other 4 products from thlis bundle are working fine, just Sound Forge Pro 13 serial number looks like it was activated by some other email that I have no knowledge of.