Can’t see /tmp/printer and not connect
Klipper by default adds a link /tmp/printer pointing to the correct device to connect to. If that link is owned by a different user then repetierserver and the /tmp folder has the +t flag set, we can not read and open the link due to permission problems. In that case you can either reference the device directly – normally /dev/pts/1 and everything will work.
If you have multiple klipper instances so it is not clear which device will point to which pts device, you can klipper where to place that link with -I flag. Default is in /etc/defaults/klipper and can be changed there. So create a folder writeable by Klipper, e.g.
sudo mkdir /var/lib/klipper sudo chmod 777 /var/lib/klipper
And then modify in /etc/defaults/klipper
KLIPPY_ARGS="/home/pi/klipper/klippy/klippy.py /home/pi/printer.cfg -l /tmp/klippy.log"
KLIPPY_ARGS="/home/pi/klipper/klippy/klippy.py /home/pi/printer.cfg -l /tmp/klippy.log -I /var/lib/klipper/connect"
And then also enter /var/lib/klipper/connect manually in Repetier-Server port name. After restarting Klipper Repetier-Server should now see the link and open it without problems.