If you get "?" back from the printer, it means the SGD command you issued is not supported by the version of the firmware on the printer. To see which SGD is supported, you can use the following commands to retrieve all configuration variable, and check the SGD you use against the response.

### Retrieve all configuration variables
! U1 getvar "allcv"

### Equivalent SGD command in JSON format.
{}{"allconfig":null}