Here are steps how to listen to Audible audiobooks.

STEP1. Here is how to pair the Interval with the Watch:
When connecting the watch to Interval make sure the Bluetooth on your phone is off.

If you have previously tried to pair the Interval with your watch - check these steps first to un-pair it.

1) Please 'kill' all the running apps in the watch and restart the watch. 

2) Go to Watch Settings > Bluetooth > find the H2O Interval. Tap the Info icon and the select the FORGET THE DEVICE. Now you have unpaired the Interval. 

Then let's try to repair it again with the steps below.  

1) Power off the Interval

2) Power off your watch and the power it on again.

3) Now make sure the Bluetooth on your watch is on. On your Watch go to - Settings - Bluetooth - and the watch starts to look for devices. (If you already see the H2O Interval - click on that - and select - forget it.)

4) Now quickly Press and hold the center button until the light blinks red and blue. You will also hear an audio prompt which says, " pairing".

5) When you see the H2O Interval appear on your watch tap the text to complete the connection.

Here is a video:

Apple support on pairing BT headphones to Watch:

STEP2. AUDIBLE App steps:
Here is a complete list of steps.'ve%20paired%20your,t%20already%20paired%20your%20headphones.

Here is a good video to help:

Audible support: