Lennox WP18 Humidifier w/ Pro1 IAQ Humidistat

Furnace - Lennox 2 speed G60
Humidifier - Lennox Healthy Climate WS18
Thermostat/Humidistat - PRO1 IAG T955 WH

I just had the humidifier installed, and the installer also put in a manual humidistat. The humidifier will only activate if there is a call for heat.

My goal is to wire the humidifer to my Thermostat/Humidistat such that when there is a call for humidity, it will activate the furnace blower and activate the humidifier.

So I bought a 24 VAC relay and wired the H and C terminals (of the thermostat) to the "coil" side of the relay. The other 2 terminal of the relay got wired to the humidifier.

When I did this, the furnace blower would turn on when there is a call for humidity, however humidifer fan would not activate.

I had a Honeywell Truesteam humidifer and used the same wiring configuation and it worked fine. I am just not sure why this will not work correctly. I can say that the relay I'm using is brand new and I checked the voltage going into the relay and there is 28 volts going into the relay (according to my volt meter).

Any suggestions would be appreciated.