Hi, the supervisor is using the LED and this may interfere with how your service can use the LED device. Some users have been asking for this feature to allow their service to control the LED. We have created an issue to track it here: Allow the ability to tell the supervisor to not use the on device LED · Issue #1375 · balena-os/balena-supervisor · GitHub.
A particular workaround from the community is to modify the /etc/resin-supervisor/supervisor.conf file in the HostOS and setting LED_FILE=/dev/null. This should allow your service to use the onboard LED device. I hope this helps while a permanent configuration path is not yet available.