GitLab Push Mirroring - Branches on Remote GitLab are not deleted

Hi,

i’ve been setting up a push mirror to a remote GitLab Server.
Used the docs, everything worked fine.

New Branches, Tags and commits are transferred to the Remote just perfectly.
But the thing is, old FeatureBranches that have been merged and don’t exist anymore are not deleted on the remote?

It’d be awesome if someone could lend me a hand here.

Thank you in advance …
Rene