Old iPhone SE given to son

Hi

I have recently purchased a new phone/contract for my son and i am giving his old phone to my mum. I reset the network settings in error as I meant to reset and delete all context. I have since done this so the iPhone SE is now in reset / new set up mode. However as i try to activate this I am getting the following message:

could not activate iphone

your iPhone could not be activated because the activation server is temporarily unavailable. Try connecting to iTunes to activate it or try again in a few minutes.

If problem persists contact apple support.

The problem does persist and I am contacting you for assistance