Triggering a webhook URL on merge

Hi there

I’ve setup a webhook in integrations that is triggering a build process on our jenkins server. The build is hideously long(working on that), so I only want to trigger the build when a merge request into a certain branch is merged. Not when a merge request is created, or anything other than a merge request being merged.

I can’t see an obvious option for that on the Integrations page.

I could well be doing something daft though.

Could someone help me out?