When you say you added AZW3 to the list of formats, do you mean you added it at the source code level or merely in the configuration screen? It needs to be added to the the source code level for it to be effective.
For the next release several changes are in being made
- the validation of the configuration screen will highlight any formats that are not on the list that Calibre2opds has built into the soutce code and thus knows about by default.
- it will be possible for the user to extend the list of known formats by updating a configuration file rather than having to make a change to the source code and rebuilding calibre2opds.
- azw3 is being added to the list of formats Calibre2opds knows about by default for generating correct download links.