K8400 filament sensor

Hello, there are still some free entries on the board, it is possible to integrate a filament sensor. according to firmware, he is indeed supported, unfortunately, you will not find a post on which pin you should put the sensor. can someone help me?

I do not own a K8400 but the Vertex Delta K8800 has a Filament sensor. Maybe you want to have a look in K8800’s schematics for inspiration: