There could be a couple of reasons your Water Main Shut-Off isn't pairing with your hub.
The Unit Needs to be Reset
Sometimes, our testers might forget to exclude the device from the testing Hub at the factory after performing quality control testing. The LED Indicator should be blinking constantly up until it's included in a network. If it's not blinking, reset your device by powering it on and pressing and holding the Button until the LED starts to blink. Then try including it one more time.
You're Out of the Range Of Your Hub
You might be too far from your Hub for the Water Main Shut-Off to communicate reliably. Try the inclusion process close to the hub to rule that out. If that's the case, add some plugged in devices between your primary controller and desired installation location to boost your Z-Wave coverage, and try again.
You're not Feelin' the Rhythm
When you include the Water Main Shut-Off, the button has to be triple-tapped in a very specific rhythm, approximately 3 times in one second. If it's not tapped correctly, it won't include - see the Figure 1 below. If done correctly, the LED will stop blinking and remain on if the Water Main Shut-Off is closed, or off if it's open.
Figure 1 - Tapping the Button Correctly