back Camera error , wont work

If there's not any reason for the physical cameras to be messed up (water, heat, or impacts, to name some), I would look for any settings that might disable specifically the back camera, for some reason:

• Firstly, swipe down into your Quick Settings (notifications area), look if there's a button for "Camera Access", make sure it's on, or that any other option like that in there isn't blocking your camera.
• If you've manually gone through enabling Developer Options, follow the rest of this portion. Make sure "Sensors Off" isn't enabled, which can be seen as a button in your Quick Settings if you've changed it to be pinned there. If you have gone through Developer Options but never pinned that function, find one of the menus in there along the lines of "QS Developer Tiles" and see if that same "Sensors Off" option is enabled there.

There could also be an issue with the camera app. If it doesn't work in other camera apps either, then it isn't likely just that app.

Otherwise, it may be damaged or malfunctioning. If you know there wasn't an accident with the phone that could've caused that, make sure any previous owner of the phone didn't experience an accident with it. Sometimes, an accident that happened a while ago can result in issues that appear down the line.

If you got the phone from a carrier, a store, or TECHNO itself, you might need to see if you have any warranty on the device, or you could contact TECHNO. Before you do any of that, though, double check that your phone doesn't have any software updates. It may've been a faulty update.