Quick linguistics lesson. They speak Macedonian in Macedonia. It's actually way less similar to Serbian than Montenegrin or Bosnian are. There's seems to be more Russian-Bulgarian influence, I guess. I'm no expert, of course, but the differences are pretty striking.

Менувачница instead of мењачницы.
Театар instead of позориште.
Сметка instead of рачуна (bill).
Кафе за носење instead of за понети.
And there are tons of these substitutions.

To completely break the system, they use ќ instead of ћ. For example, their word for house is куќа, not кућа. Or ноќ instead of ноћ. And they basically dropped the letter х from the beginning of some words entirely. I had to buy леб and алву.

Still, even with my modest Serbian knowledge, we could understand each other just fine. At one point I tried switching to English when I was checking into my accommodation (it was really hard to express myself in Serbian). But they replied with "let's just stick to Serbian."

There are some fun brain teaser exercises. I didn't immediately figure out how to translate "Враќаш толку колку што си зел," but then it clicked (:

PS. Wikipedia has a whole section about whether Macedonian should be considered its own language. They write that throughout history it was considered a Bulgarian dialect, then a Serbian dialect. And only in the middle of the last century did it start being considered a separate language. But Bulgarians still think it's "the Macedonian norm of Bulgarian"!