Honeywell Vista 20P requires an Alarm.com System Enhancement Module (SEM) in order to connect to Alarm.com. The SEM is the 4G LTE cellular module and Z-Wave radio.
We do not carry it but the SEM300 is the most recent version of this device.
More information on pairing this device, including which models are compatible with Alarm.com, can be found below:
Otherwise, you can replace the system with a Qolsys IQ Pro, or an IQ Panel 4 and a Hardwire to Wireless Translator.