iPhone SE is not compatible with cellular Watch 3

Hi

iPhone SE is compatible with Apple Watch Series 3 (GPS + Cellular), which have a red dot on the Digital Crown, and also with GPS-only models:

Identify your Apple Watch - Apple Support

Follow the instructions here to pair and set up your Apple Watch, being sure to first update your iPhone to the latest version of iOS if you have not yet done so and, if necessary, contacting Apple Support for assistance, via the link in the article:

• Set up your Apple Watch - Apple Support
• Update the iOS on your iPhone, iPad, or iPod touch - Apple Support

In order to also set up and use the built-in cellular feature on Apple Watch Series 3 (GPS + Cellular), you will need a compatible service plan for your iPhone from a supported carrier:

Apple Watch - Carriers - Apple

Follow the instructions here to do so:

• Set up and use cellular on Apple Watch Series 3 (GPS + Cellular) - Apple Support
• Use Apple Watch with a cellular network—Apple Watch Series 3 (GPS + Cellular) only

If you still need help, then I suggest that, in the first instance, you contact your carrier for assistance with setting up and using the built-in cellular feature.

If you need further help, then, depending on your carrier's advice, I suggest that you next contact Apple Support (remote diagnostics and/or mail-in service may be available, if required), make a Genius Bar reservation or visit an Apple Authorised Service Provider for assistance:

• US: Apple Watch Service Answer Center - Apple Support
• Elsewhere: Apple - Support