AppImage: Bluetooth-serial rdtech-um device - no connection without root privileges

[lassaswor74]

I'm using SmuView-0.0.6-git-7050317-x86_64, appimage version on Linux Mint 20.3. I'm trying to connect a RDTech UM34C usb power meter via bluetooth-serial (driver rdtech-um).

With SmuView running as root all works just fine. First, I have to connect the um34c via blueman so the serial connection via /dev/rfcomm0 (rfcomm0) is possible. Device is found and all is ok!

When running Smuview as regular user, serial connection via /dev/rfcomm0 is detected but no device is found and this error come up via terminal: sr: serial-libsp: Error opening port (13): Permission denied

I've already added the udev rules as the SmuView user manual suggests, but with no luck.