i second hand bought an iphone and it’s stuck on activation lock what do i do ?

Activation Lock is intended as a theft deterrent.

It is intentionally not easy to bypass.

Nothing you can do with this, given you’re asking here and given the seller is gone.

Maybe a police report, or seller feedback, but nothing that will make this iPhone usable to you.

Probably a lost or stolen iPhone, too.

We can’t help with Activation Lock.

Apple won’t.

You got scammed.

Recycle the iPhone.

The All Too Common SAD Reality of Buying a used iPad/iPhone - Apple Community

you will need to find that person and have them unlock it.. or the phone will not be usable

How to remove Activation Lock - Apple Support

Please return the phone for a refund, as it is useless unless the original owner has unlocked the phone.