Retrieving file metadata of a document through API

[Cornellius]

Hello,
I probably forgot something or I'm doing something wrong because I cannot view the file metadata of a document when I retrieve the metadata through the API (GET /documents/{document_pk}/metadata/). I receive the document metadata without problem. I verified that the file metadata have been properly extracted.
Is there any setting I should check or a specific URL I should use ?
Thank you and take care.