iphone 7 not working

Dear,

Greetings

My iphone 7 is not showing home screen after formatting it.

When press on button it shows hello,,,language..country,.etc then "it will take few minutes to update your iphone" but some time later it shows "your iphone could not be activated because the activation server is temporarily unavailable. Try connecting your iphone to a Mac or to a PC with ITunes to activate it or try again.."

SN. 17SJ6BBHG7J

i do not know what to do and how to do.

Kindly help.

Best regards,

Shrawan Motiani