URN plugin for monographs not working

I have problems applying URNs to monographs:

  • I activated the URN plugin and filled in the neccessary fields
  • We use URNs on the level of monographs, so I checked those
  • On the publishing stage for the monograph, however, the URN field does not show up on the “identifiers” tab. There I only find the DOI field.
  • When publishing, OMP warns that a URN for the monograph is missing.

I also tried if assigning URNs for chapters would work, which seems to be the case: At least the URN field shows up on the tab for chapter identifiers. So it only seems to concern URNs on the level of monographs.

We use OMP

Any ideas?