Hi I bought an unlock iPhone 13 but having trouble activating it

See -> How to remove Activation Lock

How to remove Activation Lock – Apple Support (UK)

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

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.

Is the iPhone new? Where did you buy it? Is it activation locked to another Apple ID?

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Did you bought the iPhone 13 second hand?

And is it activation locked?

Activation lock can only be removed by the original owner, see this link for further reference