Zabbix Mattermost notification integrations - Timeout exceeded while connecting to 'localhost' when testing Mattermost Media Type - zabbix

Question

I am trying to intergrate our mattermost with zabbix to receive notifications on alerts. I've followed up the instructions on this link. We are using Zabbix 4.4 with MM 5.19.
After enabling the integration, No alerts are being posted on Mattermost. I tried testing the Media type on Administration > Media Types > Mattermost > Test.
I've added the following as the parameters, but it throws the error : Connection timeout of 3 seconds exceeded when connecting to Zabbix server "localhost".
bot_token : {Token generated for the Bot in Mattemost}
mattermost_url : {https://mattermost.our-company.com}
send_mode : alarm
Tried changing {ZABBIX_URL} to both http://127.0.0.1 and http://zabbix.our-company.com (The DNS is resolved only internally, but our mattermost is available on public network) but none of them work.
I checked the logs inside /var/log/zabbix but no error or anything. I even tried putting the zabbix logs to Debug mode but no luck in any case, the only Debug log I've got is the following :
2063:20200216:090224.146 trapper got '{"request":"alert.send","sid":"74095b240dd6783618571516f029187a","data":{"parameters":{"zabbix_url":"{$ZABBIX.URL}","send_mode":"alarm","send_to":"{ALERT.SENDTO}","event_tags":"{EVENT.TAGS}","event_name":"{EVENT.NAME}","event_nseverity":"{EVENT.NSEVERITY}","event_ack_status":"{EVENT.ACK.STATUS}","event_value":"{EVENT.VALUE}","event_update_status":"{EVENT.UPDATE.STATUS}","event_date":"{EVENT.DATE}","event_time":"{EVENT.TIME}","event_severity":"{EVENT.SEVERITY}","event_opdata":"{EVENT.OPDATA}","event_id":"{EVENT.ID}","event_update_message":"{EVENT.UPDATE.MESSAGE}","trigger_id":"{TRIGGER.ID}","trigger_description":"{TRIGGER.DESCRIPTION}","host_name":"{HOST.NAME}","host_ip":"{HOST.IP}","event_update_date":"{EVENT.UPDATE.DATE}","event_update_time":"{EVENT.UPDATE.TIME}","event_recovery_date":"{EVENT.RECOVERY.DATE}","event_recovery_time":"{EVENT.RECOVERY.TIME}","bot_token":"qs3rkqdappy6i8gs3a8871phxc","mattermost_url":"https:\/\/mattermost.our-company.com"},"mediatypeid":"7"}}'
What can be the issue? Is there a way to "debug" and find the root cause of this error? Any help is appreciated! Note that right now we have integrated Slack with Zabbix and it's working fine, but we are moving to Mattermost and therefore, we need to migrate the integrations as well.

Answer 1

We found out the issue with our Network Admin. The problem was that our Zabbix server was trying to resolve Mattermost name from local network route (i.e. 192.168.x.x) and it kept failing, therefore, no SSL connection could be initiated.
It seems that Zabbix integration tests' error messages are quite generic and sometimes, misleading. Thorough investigation is needed for finding out the root cause.