PAN-OS XML REST-API - Proxy to Firewall from Panorama

curl --location -g --request GET 'https://<ip/host>/api/?type=config&action=get&xpath=/config/devices/entry/vsys/entry[@name='\''vsys1'\'']/rulebase/security&key=<token>&target=<fw_serial>'
Example of API proxy from Panorama to firewall

Get Candidate Configuration