Maker Channel Seteup Q

Herding Lab

Onion Omega (Firmware 0.1.4 b330)
and
Relay Expansion

I am able to have the Omega relay expansion turn on/off a LED when:

connected to the Omega via serial cable
using ssh over WiFi
using the Device Explorer at cloud.onion.io

Love the form factor and am very much enjoying the user experience of having the Omega interface to other devices/expansions.

My question relates to using the Do button with IFTTT and the Maker Channel.
Specifically, when configuring the Maker channel portion to make a web request, I am using:

URL--> https://api.onion.io/v1/devices/<my device id was here>/i2c_exp/relay-exp?key=<my API key was here>

Method--> POST

Content Type--> application/json

Body--> {"command":"set","params":{"channel":"0","state":"on", "address":"000"} }
(It seems the space between the last two braces is necessary.)

I am able to click the Do button but am not seeing the Omega relay expansion react.

The link to https://sdk.onion.io/reference/onion-cloud-APIs/intro.html came tantalizing close to answering my question. Can anybody enlighten the ignorant person (me ) here?