It’s not hard to know when machines need to be refilled. You just come regularly, take note of how much or little stock has been purchased, then adjust your refill amounts and times accordingly. This has to be done regardless of a handful of computerized machines because plenty of them still aren’t.

I worked in the arcade/vending business in the 1990s. That blind maintenance model was a crapshoot for the machine owners. We had to routinely send a crew (usually me and one other person) to drive to a location - near or far - with games, photo booths, vending stuff, etc. just in case the supplies in some machine or another ran out, something needed fixing, etc. Sometimes we'd arrive and learn we have hours of refilling and/or maintenance work to do on a machine, sometimes it had been a slow week or two and a crew had just spent their whole workday and a tank of gasoline to collect $50 from the cash box and go home again. Remote administration really changed the game for that whole business.