[Mark McLeod]

Look at the status lights on the Digital Sidecar for the Relay.
The lights are in the trough in front of the Relay pins.
You should see a green LED if the software is trying to start the compressor.

Is the robot enabled from the Driver Station?
Is the Spike status light glowing orange?

There is a test program you can use to make sure it's not a code issue.
From the Getting Started window -> Support -> Find FRC examples...
Look under the pneumatics folder and pick an example with a compressor.
Change the example's cRIO IP to match your cRIO, i.e., right-click on cRIO Target and choose Properties to change the IP.

Just use the Run button to test it on your cRIO.