If you have a 25-digit Download Access Code, you must convert it into a 32-digit Activation Code: Installation and activation - Steinberg
The method for finding your code depends on how you acquired the software: Online Purchase: activation code for cubase 10.5
To activate Cubase 10.5, you need to use the eLicenser Control Center If you have a 25-digit Download Access Code,
Check your email for a "Steinberg Shop Order Confirmation." The code is included in that message. Boxed Version/Hardware Bundle: activation code for cubase 10.5