We tested the Bravo app on two devices. It appears that there may be an issue with the authentication process between the Bravo app and Cox.com. We've reported this to our TV Everywhere team for investigation.
We discovered a workaround, however. After you open the Bravo app, go to www.cox.com using your browser of choice. Click on Sign In, enter your Cox Primary User ID and password, and click the Sign In button. You should now be able to play content within the Bravo app. Does this work for you?