Are the Digital Sidecar 3 power LEDs all bright green?
Are the Digital Sidecar Relay LEDs lighting up when they should?
Off = off
Red - reverse
green = forward
red & green = On
If those aren't lighting and the Driver Station reports Communications, Robot Code, and Enabled, then your code is not doing what you think it should.
If the LEDs are lighting up properly, then it'll be between the Digital Sidecar and the Spike.