There are many reasons why your AirPods might have trouble pairing with your Bluetooth devices. Some of the possible reasons include:
Check Your Battery. If your AirPods are running a low charge, it may interfere with their ability to pair with your devices. The best way to ensure your AirPods charge properly is to place them in your charging case, then connect the charging case to a USB port or wall outlet with the appropriate Lightning cable.
Your AirPods charging case provides a quick battery level overview.