Jira intregration seems not to work

In GitLab CE 8.14 we wanted to enabled Jira intregration. All setup seems fine, but seems not to work.

A few remarks;

  • Jira Core was not a group (we use .atlassian.net), only Jira Users
  • Test button sends request, but thats it, no response.
  • Tickets are not linked

Does anyone have an idea, or know how get more information?