An elementary puzzle about ice cream machines, which many fill up

First, let's give each of the machines a name:

1. "Vanilla".

2. "Chocolate".

3. "Random".

Now let's take one coin and put it into the slot machine with the "Random" sticker. The inscriptions always lie, which means that the vending machine definitely cannot dispense random ice cream. We can determine its true name based on the taste of the dessert that will be given to us. Let's say we were offered vanilla ice cream, so this is a machine with the name "Vanilla".

Then everything is simple. There are still machines with two stickers: "Chocolate" and "Vanilla". But we've already found the source of vanilla ice cream. Thus, there are only two options left: a device that gives out a random taste, and one that is guaranteed to fill the cone with only chocolate dessert.

Again, we remember that stickers always deceive us. So the vending machine labeled "Chocolate" cannot really dispense chocolate ice cream. This is "Random".

The remaining device with the Vanilla sticker offers exclusively chocolate ice cream.

Answer: we only need one coin to understand what kind of ice cream the machines give out.