Apple Watch locked when bought it off someone

You must contact the seller (hopefully it is the previous owner), otherwise you have been scammed.

Each Apple device is linked/associated with an Apple ID of the person who did the setup.

Activation Lock prevents anyone who is not the owner from using this Apple Watch.

To unlock the Watch, you need the Apple ID and password of the previous owner, that were used during set up.

So you have to contact the previous owner.

The previous owner has to read -> this Apple article: What to do before you sell, give away, or trade in your Apple Watch, or buy one from someone else

What to do before you sell, give away, or trade in your Apple Watch, or buy one from someone else - Apple Support (IE)

Then the previous owner has to remove the Apple Watch from his account, see this Apple article:

Check your Apple ID device list to see where you're signed in

Check your Apple ID device list to find where you're signed in - Apple Support

Then you can pair the Apple Watch with your iPhone.

See the following Apple articles:

About Activation Lock on your Apple Watch

About Activation Lock on your Apple Watch - Apple Support

How to remove Activation Lock -> How to remove Activation Lock – Apple Support (UK)

• If you need help removing Activation Lock and have proof of purchase documentation, you can start an Activation Lock support request.

👉 Read this before you 2nd hand device.

You can also contact Apple support for help, -> Get Support (apple.com)

You have to show proof of ownership of your product, provide all documentation showing your purchase of the device.

If you do not have additional proof of ownership, contact the reseller. They may be able to provide the original purchase document.

Once Apple receive your proof of ownership, Apple will further review your request and provide an update.

See also Keep your receipt after you buy an Apple device

Keep your receipt after you buy an Apple device – Apple Support (UK)

-----

Ask your money back if possible, perhaps you have bought a stolen Apple Watch.

If you can't get in touch with the seller, you can't use the Apple Watch.

Accept it as a life lesson and recycle the watch responsibly.