In case the connection can not be established with the drone, ensure that:

• You can connect properly to your drone using the drone manufacturer application.
• PIX4Dscan is compatible with the drone, camera, and controller: Supported drones, cameras and controllers.
• The correct drone model is selected in the Dashboard of PIX4Dscan.
• The drone manufacturer's app is not running in the background. Force quit if necessary: How to force quit PIX4Dscan. 
• The USB cable is properly plugged between the remote controller and the iPad. Unplug and replug if necessary.
• Restart the procedure from scratch. To do so, close and force quit the app, disconnect the cable from the iPad, turn off the remote controller and the drone. Then switch on the drone and the controller, reconnect the USB cable and open PIX4Dscan.