Can’t update watchOS 8.7.1

I spoke with apple support and they are aware of this issue. Engineers are working on a fix for this and recommended trying to install it again after a factory reset of the watch in 42-72 hours. It was marked as a high priority to fix.

There is one way to get your series 3 apple watch to 8.7.1 update.

I successfully did it with my wife and my own series 3 apple watches

Pre-requisites

a) Having iphone 8 or newer, you can do it with your friends iphone just for the update, you can unpair it later( I used iphones 8, 11, and 12 models, I did not try olders).

b) iOS 15.4.1, it won't work with iOS 16 no matter how many times you try.

c) apple watch series 3 in fresh factory reset state.

Steps

1- turn updates OFF in apple watch and iPhone (both charging and WiFI)

2- delete all apps then can be deleted from apple watch, ALL.

3- pair apple watch with the iOS 15.4.1 iphone and let the process be completed

4- from apple watch go to software update and wait long time until the update is downloaded

5- go to settings, general, and tap install in apple watch (or in iphone, both of them work)

6- wait very long time (2-3 hrs) until process is completed

7- enjoy watchOS 8.7.1 fix for series 3

If you did this with somebody else's iphone, just unpair it then pair it with yours.

this works for both series 3 apple watch sizes

Yes that should work.