why I am unable to active my new iphone 8

1. Ensure that you have a SIM card inserted in your iPhone 8 Plus while you attempt to activate it.
2. While activating, did you get prompted to input an Apple ID and Password to activate the iPhone?
3. Which error do you get when you try to activate it?
4. Where did you buy this iPhone from?

A few more detailed information will help us try to guide you in the right direction. Thanks.

Axel F.

See this, If you can't activate your iPhone - Apple Support