GitLab has two methods for third-party integrations: webhooks and official integrations. Discord has an official integration page but it turns out it has a bug where the save button just hangs and doesn’t save anything, which makes adding the integrations quite annoying.
Learned through trial and error today that if you hit “Test Settings”-button before save, the save still hangs but now the integration is saved after some time.
(Was going to report this bug, but gave up and wrote this TIL instead.)