My landlord emailed me to say that the HOA prohibits any feeding of ducks and pigeons, so I took down the vending machine until I can find a suitable place for it. There is no practical way to prevent pigeons from using it.
This is too bad since it looked like the jackdaws were finally taking notice, but I don't want to contribute to the pigeon problem or have problems with my neighbors and landlord. I guess this is something to consider when you are putting something like this up.
The best places for vending machines like this are away from tthe city center, in or near parks, event venues and places people tend to gather like town squares and lakeshores, especially outside the center of a city. There are not too many restaurants to generate a steady stream of waste food and lots of people to generate litter.
Birds will only be interested in places where it's easier to find litter than food. I think many cities and towns have such places.
I think the concept is a workable one and I've been testing various versions of the vending machine for over a year, so for the time being I will shift focus to optimizing the PVC enclosure, making it a little smaller and easier to look inside, change batteries/powerbank, etc. without taking it apart. Also starting to work on programming an ESP32-CAM to enable video streaming, remote monitoring and controlling the operation and taking pictures when certain events happen. Hopefully I will find somewhere I can continue the experiment