Apple Watch Series 3 - won’t update

I have an Apple Watch Series 3 here, cannot pair / access the watch without installing the latest update.

the update goes all the way to “preparing” after installing and then says unable to download the latest update due to “not being connected to the internet” when we’ve had the watch on its charger, connected the internet and the iPhone 12 Pro being fully charged.

tried multiple times and will not work.