No 'Relation URL' when running OAI in OMP

Hi
When I choose the following OAI URL for our OJS installation I receive a link to the articles:
https://tidsskrift.dk/index.php/index/oai?verb=ListRecords&metadataPrefix=oai_dc

When I do the same in relation to our OMP the article links do not show up:
https://ebooks.au.dk/index.php/index/oai?verb=ListRecords&metadataPrefix=oai_dc


How do I solve that problem?
Our current version of OMP is: 3.1.2.1
Best
Niels Erik