Iphone unable to activate.

I just bought a used Iphone X from a friend. When i go to set it up, a screen pops up saying; Your Iphone could not be activated because the activation server cannot be reached. My SIM card works in the phone, I can see it has service. So it isn't a problem with the carrier or the sim card. I tried plugging it into a MAC, and it is still unable to connect to the phone, giving me an error message (-50). The phone is unlocked, and is not under activation lock. Please help.