"Unable to Activate iPhone" Error Message

I was having trouble using cellular data, so I backed up and restored my iPhone 7 using my iMac. I was ready to load my backup onto the phone again, but when I went through the 'activation' phase of the setup (where it says hello, with the big white screen), it came up with a big, red exclamation mark and an error message. It said, "Unable to activate. Your iPhone could not be activated because the activation server is temporarily unavailable....Try again in a couple minutes." It's been hours, I have tried any and everything I can think of- software update, another restoration, WiFi, etc. Does anyone know a way around this error message? Is the Apple "activation server" actually down? Should I go to the Genius Bar? I just want to finish setting up my phone so I can reload the backup onto it. Thank you for any replies. :)