Hold your phone approximately 10cm/4in away from the mirror and keep it steady. Your phone will vibrate once the phone is in the correct position. Make sure to keep it still. When you feel a second vibration, the photo has been taken. Done
If you don't feel the vibration, make minor adjustments to the phone's position, go slowly back and forward. You can tilt the phone slightly as well. You should also see a little preview from the camera when the phone is held up, so make sure the camera sees the QR Code.
Then review the photo displayed, ensure that your entire phone is visible and if it is, submit the image; otherwise, try the process again.