my new apple watch series 3 won't pair with my iphone xr

Make sure you update your Watch to OS 5.3 as well. If so, follow these instructions....https://support.apple.com/en-us/HT205025

If you still need help, click on the "Contact Support" link at the upper right side of this page.

That’s the problem. When it starts to update the watch iOS it causes an error and unpairs the watch. It’s not possible to complete the update.

If you still need help, click on the "Contact Support" link at the upper right side of this page.