Can I put any SIM card into an iPhone 6?

Hi, before anything else, thanks for your time. I appreciate you.

Anyway, I recently was sent a secondhand iPhone 6 by a cousin in another state. It was locked and in lost mode for some reason when it was given to me, but I had no problem restoring it to factory mode. When I did so, the only problem I have encountered so far is that the iPhone is asking for a SIM card. My cousin claims to have lost it, so I'm really just at a loss of what to do. I've found that is in fact a nano SIM card, but I want to ask for your advice on how to continue.

In lost mode eh? Almost certainly when you put a SIM card in, you will find that the IMEI (phone ID) had been blacklisted because the phose was reported stolen. You will not be able to get any cellular service.