Error when trying to activate FaceTime and iMessage

My son got an iPhone 8 for Christmas, he’s 8 so it’s just for playing games and communicating with family around Wi-Fi. Problem is, we keep getting an error when trying to use FaceTime or iMessage. We set up his Apple ID and are signed in, but keep getting the error “An error occurred during activation. Try again later” every time. I’ve upgraded the software, powered on and off and nothing is working. I can sign into my own Apple ID on his phone and it works fine though. Any advice?