Fan Shim on PI3

Hi!, on my PI4 (and buster) Pimoroni fan shim works very well but on my PI3 (and scratch) I have a problem with the software…
is there a way to make it works on PI3?

when try to activate the service I get this error. Could you help me?
thanks in advance

Failed to restart pimoroni-fanshim.service: Unit pimoroni-fanshim.service is not loaded properly: Invalid argument.
See system logs and ‘systemctl status pimoroni-fanshim.service’ for details.
● pimoroni-fanshim.service - Fan Shim Service
Loaded: error (Reason: Invalid argument)
Active: inactive (dead)

Older versions of systemctl require full paths to executables in the install script. The Buster version accepts relative paths, so that could be the problem.