Executing PRTG API commands from PRTG

We are trying to setup a backup for our main monitoring tool for our network. If it goes down, we want PRTG to be able to take over the monitoring. I don't see a way to enable/disable notifications for a group based on the status of another sensor. So I was thinking I could setup a group with the notifications already in place, pause it, and then if a sensor goes down, it sends a PRTG API command to unpause the group. And when the sensor returns to normal status, it pauses the group again.

I was trying to use the HTTP Action to unpause using the API, but it doesn't work. The log shows this: State Trigger sending HTTP (Sensor/Source/ID: 35491/35490/2), no errors.

The notification template is setup like this: URL: http://prtg.mydomain.com/api/pause.htm?id=35491&action=1&username={username}&passhash={passhash} SNI (Server Name Indication): Do not send SNI (default) HTTP Method: GET (x) POST PUT PATCH Payload ____

Any suggestions would be much appreciated! Thanks!

api prtg sensor