Thanks for all your work. I figured I just misunderstood you. Deutsch?

Looks like you are doing everything correctly which probably means I am the one doing something wrong.

The fact that even MatchDevicePath "/dev/ttyS0" alone doesn't work is probably a big fat clue if I can figure it out.

I have v2 back up for you to test. Compiles without the error anyway.

Sleep well. Tomorrow then.