Installing Cubase 4.1 on older Mac

I found a Tascam US428 interface/controller in my basement. Went through all my Macs to see which would install the most recent driver (2007). Turns out my G4 Powerbook!

I have used Cubase all the way up from V1 (actually before when it was on OS9). But I can’t figure out how to get the licensing to work. The licenser asks for a 16 digit activation code - all I have is a nine digit serial #.

Any ideas welcome!