This is an iOS clone of SIMPLY-2943, which was fixed on Android.

The circulation manager is telling the client to expect this media type:

application/audiobook+json;profile="http://www.feedbooks.com/audiobooks/access-restriction"

The Feedbooks server is serving a slightly different media type:

application/audiobook+json; protection=http://www.feedbooks.com/audiobooks/access-restriction

This difference is not big enough to justify treating the data as an unsupported media type. SimplyE should be able to take any kind of "application/audiobook+json" (or application/json, if it comes to that) file and treat it according to the rules the CM laid down before handing the client off to the vendor.