The ChatterPix app is designed to be used upright in portrait orientation. If you rotate the device to landscape orientation before taking a photo, an error might have occurred.
If you are having trouble taking a photo or finding the camera button, please close the app, hold the device upright in portrait mode, and then start the app again.
If the orientation lock is on and set to landscape mode, swipe up to open the Control Center, and turn off the orientation lock (the icon for managing orientation/rotation looks like a lock inside a circular arrow).
Return to the ChatterPix app. Ensure that before pressing the “Take a Photo” button inside the app, the device is being held upright in portrait orientation.
Additionally, if restrictions are enabled on the device, those restrictions could be prohibiting access to the device's camera. To check, go to the device's Settings app, and select Settings > Privacy and Settings > Restrictions to ensure ChatterPix has access to the device's camera and photos.