The alarm that occurred was disarmed during the system’s delay period. As such, the alarm signal was not forwarded to the monitoring station.
You can confirm this in Alarm.com > Recent Activity. You’ll see the sensor that triggered the event Pending alarm (awaiting panel’s programmed delay)
This is due to Dialer Delay, which is a period after an alarm is triggered by a sensor on the local system and the alarm signal being forwarded to the central station. This is enabled to help combat false alarms.
More information about this, including how to adjust the time for your system can be found here:
Steps on how to test your alarm system to ensure proper function can be found here:
Also, you can find more information on how to utilize 24/7 Professional Monitoring can be found here: