Did you try the examples here?
https://sc1.checkpoint.com/documents/latest/APIs/index.html#cli/gaia-api~v2%20
I assume you have checked that the Gaia API is working properly on the final target with gaia_api status?
Next step is to look in $FWDIR/log/api.elg on the SMS for clues, and also on the Gaia target the log file /var/log/gaia_api_server.log. In many cases while teaching the CCAS class, looking at these log files is the only way to figure out what is wrong due to syntax /parsing errors and such.
Gaia 4.18 (R82) Immersion Tips, Tricks, & Best Practices
Self-Guided Video Series Coming Soon