Jira 8 and Gitlab 12 CE

We have a Jira Software on premises instance and a Gitlab running version 12-CE. I’m following the guide here for showing branches/commits etc in Jira ticket:

However no matter what I try gitlab always returns a 404 when Jira tries to do the token exchange. In gitlab I have the application setup for a user and the redirect url set as:

Is this setup correct? Or does the intergration not work between these latest version of Jira and Gitlab?

Appreciate any help anyone has.