Apple Id not working on iPhone

Make sure that your iPhone, iPad, or PC has a strong internet connection and that you've turned on cellular data on your iPhone or iPad by going to Settings> Cellular or Cellular Data. With this setting turned off, you may not be able to access your Apple ID and iCloud if you are not connected to a Wi-Fi network. https://www.wikicue.com/apple-id-not-working-on-iphone/