Unable to transfer audiobooks to Apple Watch

Apple Watch Series 3

iPhone 7

Both have latest updates

I am unable to transfer audio books from iPhone to watch. audiobooks are stored on the iPhone, and show in the Books app, but not on the watch audiobooks app.

I have tried using audible to transfer. I am able to select the option to sync, but after reaching 100% the audiobook does not show in the audible app on the watch.

All the apps are up to date. I have tried restarting etc.

please help