When you attempt to authenticate with the DUO Mobile application on your iPhone you receive the error message "Account Error. Something unexpected happened. Please contact your helpdesk. NSURLErrorDomain -1200 (code may vary)."

iOS, DUO Mobile
Switch to a different WiFi network or turn off your iPhone's WiFi to force your device to use cellular data and try to log in again.
NSURL is a legacy service on iOS devices and can prevent Duo Mobile from connecting to a network properly.
Disabling WiFi, or connecting to a different WiFi network, will allow you to successfully authenticate within the DUO Mobile application.