I Didn't Get an SMS Text
This article provides possible causes and solutions if you do not receive a code when you choose to authenticate via text message.
Problems receiving text passcodes from Duo could be due to one of the following:
Weak Cellular Connection
Make sure that your cell phone connection is strong. If your cellular connection is weak, please find a place where you have a better connection. If you are using a smartphone, you may be able to improve your cellular data connection by turning Airplane Mode on and off. This will reset the connection and then you will be able to receive the authentication text.
Problem with Your Device
If your phone connection is good, but you still don’t receive a text, there might be a problem with your device.
Access your Duo account online.
Go to “My Settings & Devices.”
Verify that the phone number that you entered is the correct one.
In addition, underneath the list of your devices, check for the “Default Device” and make sure that the correct device is listed as your default.