Currently, triggers based on PR status are not directly supported due to differences in how different Git providers manage PR statues.
You can, however, use other trigger controls to mimic this. For example, use PR labels or PR comments such that PRs with specific labels or comments can trigger builds.
Thanks for your answer!
Triggering builds based on comments and labels is not exactly what we’re trying to do.
We found out that there is an open-source bitrise-webhooks project on GitHub that should be used behind the scenes if I’m not mistaken.
We’ve created a Pull Request that adds the possibility to trigger a build when a reviewer approved a PR for Bitbucket Server.