I have an iphone 7 and I am trying to pair it with an apple watch series 8 but can’t

I have an iphone 7+ and I am trying to pair it with an apple watch series 8, but can’t.

iPhone 7 Plus run iOS 15.7.7, can’t be update to a higher iOS.

Apple Watch Series 8 requires an iPhone running iOS 16 or later. 

See -> Set up your Apple Watch

Set up your Apple Watch – Apple Support (UK)

• To set up and use a new Apple Watch, you'll need an iPhone 8 or later with iOS 16 or later. 

You have 14 calendar days to return an item from the date you received it, if you want to return the watch, see ->

Returns & Refunds

The link on top of this page which you had visited, before posting this question here, is shown under the "Related Article” that may have given you an answer.

Select the appropriate watchOS from the dropdown menu in this guide --> Set up and pair your Apple Watch with iPhone – Apple Support (UK)

Unfortunately the Apple Watch series 8 needs iOS 16 to pair to a iPhone but because you have a iPhone 7 Plus which can only be updated up to iOS 15.7.7 you’re best bet is either returning/selling the watch or upgrading your iPhone to a iPhone 8 or higher.