If books are in the appdef file but cannot appear in the interface. how to solve it?

<books id="C01">
    <book-collection-name>Main Collections</book-collection-name>
    <book-collection-description>Alkitab Versi Borneo</book-collection-description>

i have this, but can’t appear in the interface

Hi Elan,
Welcome to the community!
I need to ask a few, clarifying questions:
Do you have only the one book collection in your app?
Do you have books added to the collection?
What appears in the Viewer tab if you click on a book in SAB.
If you build an APK and install on your phone, what are you seeing when you run the app, if anything?