How to pair my Apple Watch 8 with iPhone

Is your iPhone running the latest iOS version? If not, it might be unable to pair an Apple Watch running watchOS 10

See this on how to pair Apple Watch

1. ut your Apple Watch on your wrist. Adjust the band or choose a band size so your Apple Watch fits closely but comfortably.
2. For information about changing the band on your Apple Watch, see Remove, change, and fasten Apple Watch bands.
3. To turn on your Apple Watch, press and hold the side button until you see the Apple logo.
4. If your Apple Watch doesn’t turn on, you might need to charge the battery.
5. Hold your iPhone near your Apple Watch, wait for the Apple Watch pairing screen to appear on your iPhone, then tap Continue.
6. You can also open the Apple Watch app on your iPhone, then tap Pair New Watch.
7. Tap Set Up for Myself.
8. When prompted, position your iPhone so that your Apple Watch appears in the viewfinder in the Apple Watch app. This pairs the two devices.

Here you are. Your iPhone requires iOS 17 or later.

Set up your Apple Watch - Apple Support