How do I get the Yongnuo YN560 III flash to work with a canon eos 4000d camera?
The EOS 4000 lacks the center contact in the hotshoe. This makes it incompatible with a simple manual flash like the YN560.
Only Canon flashes, (and some 3rd party ETTL flashes) will work without the center contact.
It would be possible to use the YN560 off camera if you use some kind of compatible trigger/receiver combination.