Apple Watch pairing with a new phone
I am trying to pair my Apple Watch with my new phone and when I enter my Apple ID and password it states it is incorrect. I signed into my account online to verify that my Apple ID is correct as it my password.
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Check that you are signed in with that Apple ID on your iPhone and that it is connected to network, under Settings > Apple ID. Restarting both devices may help too.
There are further troubleshooting tips in this article as well:
Set up and pair your Apple Watch with iPhone - Apple Support