My verification code does not work?
Verification codes can appear to be invalid for a few different reasons. These are the most commonly encountered:
Check that the time settings on the device are synched. A manually set time on a phone can be off by a few minutes and this will make the verification requests appear invalid to the central server. Try setting the time automatically using the network. iOS: Settings->General->Date & Time. Android: Settings->Date & Time.
Check that the device has internet access. If it is a WiFi network, some companies and hotspots will have captive portals requiring the user to authenticate before use. Change to a different network or onto 3G and try again.