iPhone Air with iOS 26 won’t pair with Apple Watch Series 9 even after unpairing old phone

Restoring the new iPhone from the backup of the old iPhone before you pair the watch to the new iPhone is one of the key points in this process:

Pair your Apple Watch with a new iPhone - Apple Support

Maybe you should pair it to your old phone, then do this:

1. Update the WATCH to watchOS 26.
2. If the iPhone is too old, try to find another iPhone that will update to iOS 26.
3. Hopefully when the watch is on watchOS 26 then it will work.

If it is already on OS 26, then this may be an iPhone sync problem. Try getting the iPhone itself to reset and hopefully by doing those steps, your issue will be fixed!

LITERALLY same exact experience but I have a 15 pro max. Tried reboots, factory resets, contact apple support 3 different times. They even sent me a replacement iPhone because we thought there might be an issue with the Bluetooth antenna. Nothing. After 3rd contact, finally decided it’s time to go in person. Best option was a Best Buy. In 2 days. I’m having all kinds of issues between phone (ios26) and watch (os26) and phone and third party devices (Tesla, HidrateSpark).

Glad, that it finally worked 🙂

As a note for other users:

It is also mentioned in the article, updating both devices before starting the process will make sure, that the backups also contain all needed information and are compatible with brand-new devices like the just released iPhone 17 series.

Definitely try updating the watch to watchOS 26. Same thing happened to my friend and this is what she did.