“/publisher” is not recognised as a valid route by the edX MFE so you won’t be seeing anything.
You can configure the branch to pull from in tutor by setting the version parameter. The build might still fail, I haven’t tried it in Maple.
MFE_APP:
name: publisher
repository: "https://github.com/edx/frontend-app-publisher"
version: "master
port: 18400