Is it an Alarm.com branded Skybell HD or a regular Skybell HD? The Alarm.com ones have a special firmware on them to work better with Alarm.com.
Here’s a note from the ADC knowledge base:
If the Alarm.com Wi-Fi Doorbell Camera is enrolled into the Skybell app, the firmware version of the Doorbell Camera changes to a version that is not compatible with Alarm.com.
Caution : Enroll the Alarm.com Wi-Fi Doorbell Camera into the Alarm.com app only. An Alarm.com doorbell camera that was previously enrolled in the Skybell app is not guaranteed to successfully enroll in the Alarm.com app, even after it is removed from the Skybell app.
I’m not sure if you’ll be able to get that one working with Alarm.com even if it was an Alarm.com model based on the warning. It’s been a while since we’ve checked but we’ll look again into whether there’s a way to put Alarm.com firmware back on the camera.