Guidebook-1.15.2-3.0.5 will not open.

Linux Mint 19.3
ATLauncher
Oracle Java 8 (1.8.0_212)

I've looked over your docs and I think I'm getting close to having your guidebook.xml to work.
This is my directory structure:

My books.json contains:

[ "gbook:books/guidebook.xml" ]

What am I missing?
I look forward to hearing from you and greatly appreciate the help!

Thank you,
CM

PS: It would be very helpful to have a working example included with your mod.