The way that DB works (for the past couple of years now) is that it Launches the DB app to get "permissions" from it. If it is trying to launch the DB app, you must have that on your device. Try launching the DB app directly and see if it works or if there is some issue with it. After that, try TM again to see if it will correctly talk to it and if it seems like the DB app is working. If it is not work, try doing a Reboot of the device. Sometimes iOS gets stupid and things don't work as they are supposed to. I guess that absolute worst case would be to delete the DB app, in which case TM will try validating with DB by using a webpage instead of the DB app on your device. You could reinstall the DB app afterwards, however you would have to sign in again as it's settings will be deleted along with the app, so try the above things first.
