New wireless temperature sensor showing as off-line

Hi all.

Followed the install instructions - pressed the button for 3 seconds but nothing happens on the display. The device then does show up under rooms and devices if I back out out of the installation screen, but is offline.

This is the second unit I've had the same problem with.

The internet bridge is in pairing mode and I'm sitting just a few feet from it, so shouldn't be a signal/range issue.