JIRA integration: no comment in jira ticket

I just set up the Jira integration on our gitlab ce local installation towards our jira server local installation (two different local machines).

If I push a commit on the gitlab server mentioning a ticket, in the gitlab web ui I can see the referenced ticket and click on it to open Jira, no issues there, but no comment in jira gets added.

I followed the configuration here https://docs.gitlab.com/ee/user/project/integrations/jira.html the difference is the username of the user I use to connect and the group, which are some other user and group I have for this purpose, but I do not think that this has an impact. I tested the api url and user/password I configured, using soapui, and they work fine.

In the project configuration when I check and save the jira integration I see a message about the validation of the certificate (which is self signed), but I saved anyway (Test failed. SSL_connect returned=1 errno=0 state=error: certificate verify failed (unable to get local issuer certificate))

How can I disable the certificate validation on this part? I see that this can be done on webhooks for instance.
I assume this is what is causing the issue. Otherwise, has anyone any idea about this?

Some details
Jira server 7.13 self managed
Gitlab 13.0.1 self managed

Both 2 machines are ubuntu server 18.04

All certificates in use are self signed.