Why can’t I sign into my Apple Watch with my Apple ID?

Hi

Apple Watch is automatically associated with and signed in to the Apple ID account that the paired iPhone is signed into at the time of pairing.

I suggest that you unpair and then re-pair your Apple Watch to your iPhone, having first checked that you are signed in to your Apple ID on your iPhone:

• Unpair your Apple Watch and iPhone - Apple Support
• Set up your Apple Watch - Apple Support
• Apple ID