question: iOS VPN Connection – Please enter your authentication information
answer: 
  If you restart your iOS device while connected to ExpressVPN, you may encounter this message: “VPN Connection – Please enter your authentication information.”
  
  This is an iOS bug and is not an issue with the ExpressVPN app. To resolve this issue:
  
  Do not enter a password when prompted.
  Tap Cancel.
  If the “VPN Connection – Please enter your authentication information” message appears again, go to Settings and toggle Airplane Mode on.
  Launch the ExpressVPN app. Tap Options.
  Tap Other settings > VPN protocol.
  Tap Lightway – UDP or Lightway – TCP.
  On your iOS device, go to Settings. Toggle Airplane Mode off.