Webhook sending issue

[donalinsight]

I've been trying to get webhooks to work for me on a on-prem instance of Jira v7.9.0

I've configured a test webhook to fire when issues are updated. Interestingly the webhook reports as fired when I check the logs

cat /opt/atlassian/jira/logs/catalina.out

...

2018-05-16 15:17:19,745 Web-Hook-Publisher-0 DEBUG testuser 1037x139070x1 140f9vr 10.10.10.240,192.168.1.10 /secure/QuickEditIssue.jspa [c.a.webhooks.plugin.PublishTaskFactoryImpl$PublishTaskImpl] Posting to web hook at 'http://10.10.10.10:5000/?user_id=testuser&user_key=testuser', body is:

...

I figured this has to be network issues but I could curl and telnet from the host server to the receiving application on that port no problem. I checked using https://webhook.site to eliminate a port in the URL as a potential issue but it also receives nothing

I eventually took a tcpdump and went looking in wireshark for traffic outbound from the server and could see nothing relating to that connection. So the log says it has been sent but the application hasn't sent it that I can see. No iptables or anything enabled on the server

Is there a plugin, dependency or any additional configuration needed for webhooks to work?