If no hostname use IP address in URL in the http://IP/ format. Please make sure XSOAR server can connect to FortiSandbox server. 

Recommended playbook to use to upload file for analysis and get report:
Detonate File - FortiSandbox

Notice: Submitting indicators using the following commands of this integration might make the indicator data publicly available.
- ***fortisandbox-url-rating***
- ***fortisandbox-upload-urls***
See the vendor’s documentation for more details.