If you try to take a photo of your patient and all you see is a black screen, it means that you need to change iPad settings to allow Smart Flow access your camera:

To do that, open Settings on your iPad:

Scroll down and on the left column select Smart Flow application:

On the right hand side, you can change the permissions for the Smart Flow. Make sure that the knob for camera is ON (the green part is visible):  

Now when you go back to Smart Flow, you should be able to take a photo easily.

We hope that this will help you solve your issue!