Hi @Tina_Williams-2! I'm not at that point in the game yet so the best I can do is give you the link to a video for 4407 that may be helpful! Here it is:
I am also not at level 4407, but the trick to making keys drop would appear to be movement. That is, on the levels I have played that require keys I have found that you need to keep the key dispenser moving. The more movement the better.