The most likely cause of a blank screen is that the app might not have permission to use the camera. 

When the StepJockey app is first installed it should ask if it can use your camera, and you need to allow it to let the app function.

To allow the StepJockey access to your camera:
1. Go to Settings
2. Scroll down to and select the StepJockey App
3. Allow StepJockey to Access Camera

For more information, see Scanning and Tapping.