Fulfilling an audiobook from RBdigital works fine (except for the problem detailed in https://jira.nypl.org/browse/SIMPLY-2859), but fulfilling an audiobook chapter, or fulfilling an ebook, both lead to the same problem:

{"status": 400, "debug_message": "NoAcceptableFormat", "type": "http://librarysimplified.org/terms/problem/cannot-fulfill-loan", "detail": "Could not fulfill loan.", "title": "Could not fulfill loan."}