Your daily dose of riddles :)

I received this one from a friend on whatsapp and it took me some time to figure it out :). When you know the answer, please don't post it below, just comment how long it took you without cheating ;)

3 guys walk into a bar.

They order a giant pitcher of beer, for the cost of 30 bucks, and each put down 10.
The bartender takes the money and they guys go sit at their table.

The bartender shortly after realizes that he made a mistake as the price for the pitcher of beer was actually 25, not 30.
He ponders what to do, as he only has 1 dollar bills, and he can't share 5 bucks between 3 people equally.
He comes up with the idea to tell the guys that the beer was 27, and not 25, as it really was, as this way, he can just give em back a buck each, and bank the remaining 2. He gives the guys each their bill, and they all praise him for his honesty.

So, the guys originally paid 10 dollars each. They each received 1 dollar back which puts them at an expense of 3x9=27 dollars between them.
The bartender who gave the money back kept the 2 bucks for himself.
But if they guys each paid 9, and the bartender has 2, that equals 3x9 + 2 = 29. The price was originally 30 bucks.. where is the last dollar?

29=30? Or are you missing something?

image source: https://www.thedrinksbusiness.com/awards/the-global-beer-masters-2017/