Webhook not firing on older version of Jira


I’m developing an API to connect an older version of JIRA (5.2.6) to another web application. However, the Webhook from JIRA does not seem to work. The POST callback from the webhook is not being triggered at all.

My endpoint can receive POST callbacks from other applications, I have tested it with either Postman and the other Web Application, but JIRA’s webhook cannot reach it (or rather, is not being fired).

I’m unsure of this is an endpoint problem (unlikely to be), or a problem in the JIRA Server that prevents the webhook to fire.

Settings on the JIRA Webhook (created via user administrator):
Exclude details: No
JQL: project = Tests
Events: All issue events
Transitions: No linked transitions.

Any ideias/suggestions for this situation?