Philips doesn’t make this super clear but if you buy a used Hue bulb or get one from Amazon Warehouse, they often won’t pair no matter what you do.
The trick is to use a dimmer switch surprisingly.
From their site:
Factory reset a Philips Hue light
Sometimes an issue with a Philips Hue smart light can be fixed by factory resetting it with the Philips Hue dimmer switch:
- Power cycle the light: switch it off, wait 15 seconds, and switch it back on.
- Hold the Hue dimmer switch within six inches of the light [bulb].
- Press and hold both the ‘ON’ and the ‘OFF’ button for at least 10 seconds until the LED indicator on the switch turns green.
For me, it also helped to unplug the bulb once more after this, then plug in and repeat the process. Then adding via using the serial number has a 100% success rate.
I pulled my hair out for a few days until I discovered this!