My new iPad Air rear camera just shows black and won’t work. Front camera is fine. Help please! Simon.

I have just got an iPad Air Gen 4. The front camera works fine, but when I switch to the rear camera there is just a black screen and the ‘take picture’ button is unresponsive. Is there something I am doing wrong (I am fairly familiar with iPad cameras and have been using an older iPad for years. Thank you.

Note: the choice given to name your device (below) is out of date and does not list the 4th generation 2020 iPad Air!