Hi @Bob_M, just a note that I moved your post to the Duo Mobile app forum since your question concerns adding a second device for use with Duo Mobile. This will help others find the answer in the future.
Sorry to hear you’re having some difficulty with this! What type of account are you using with Duo Mobile? For example, do you use Duo to authenticate when logging into a work or school account? If this is the case, and you see the Duo Prompt with the self-service options to Add a New Device, you can follow the instructions here to enroll your Android phone in Duo. The barcode you asked about is displayed on the prompt near the end of the enrollment process.
If you’re using Duo with a third-party account, such as Google or Facebook, then you should follow the the service provider’s instructions to enable 2FA for that account. Typically, the service provider will give you an activation code which you can put into Duo Mobile. See the instructions Google provides here to add 2FA to your account using an Android authenticator app.
