Originally thought this might be a permission issue, since (in my Debian VM), `/dev/hidraw*` is owned by root. I added this udev rule to set group ownership of hidraw devices to 'plugdev':
KERNEL=="hidraw*", SUBSYSTEM=="hidraw", MODE="0644", GROUP="plugdev"
Anyways, that wasn't enough to get it working for me.
Next I fired up wireshark just to see if the app was even attempting to communicate with the remote, and I didn't see any host-->device traffic after starting the app. So my current theory is that there's still some permission issue that's preventing the app from writing to the device. But without the source code, only the flirc.tv folks can solve this :(
Please consider releasing the source code for this app. It's currently a disaster to run/debug on Linux (appimage isn't actually all that portable)