Promotion in fast-food outlets: Does Coca-Cola pay extra for institutions to get it?

Today I went to a bite to eat at the local fast food (yes, I know that it is not very useful, but I go there very rarely), “ Baked Potato ” is called.
I think what to order. Look, there is a menu:
- soup
- toast
- potatoes with 2 fillers
- Coca Cola
It is worth 28.75 UAH

I ask the girl seller: And instead of Coke something you can take?
Answer: Fanta

Because I do not like one thing or the other, I ordered everything the same, but separately, plus juice.
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The result was about 37 hryvnia.

Now we count. Juice separately costs 6 UAH. So lunch without juice turns out about 31 hryvnia.

Coca-Cola / Fanta is also separately about 6 UAH.

Those. if the cola menu is completely over 0.0, the difference between the menu together and individuality is still 4 UAH with kopecks, if you count the col on the price list - and even more, about 9 UAH.

What is the conclusion from here? I assume that fast food makes a discount for the complex, but still it seemed to me that Coca-Cola not only distributes its drinks for free, but also pays extra fast food to be taken.

Or am I misunderstanding something in this question?