Hi Antonio, 

I have seen customers use Jira before for on prem, however I can't remember which product/service they were using specifically (the best I can say is 'normal' Jira).  The standard integration configuration has "API Root" as an IP address, so talking to on prem (not cloud) is certainly a supported method.

It's unlikely to help, but a packet capture on the Remote Agent would confirm it's talking to the right IP/instance of Jira. 

I'm afraid all I can suggest is checking the online guide we have to make sure all prereq were done

https://cloud.google.com/chronicle/docs/soar/marketplace-integrations/jira

Andy