I found the solution! It was pretty obvious, now that I think about it. My camera is not compatible with this particular software, so I just had to find one that was compatible and then it finally worked.
I'm using an EOS 500D, I've got Windows 11 and the error message is:
The serial number you have entered is incorrect, or does not belong to an applicable product.Please check the product serial number and the applicable product to make sure it is cor...
