Why "sneak peak" doesn't quite hit the summit
What kind of error is it?

It's a spelling error.
Why do people make this mistake?
People often make this error because "peak" and "peek" are homophones; they sound the same but have different meanings. "Peak" refers to the top or highest point of something, like a mountain, while "peek" means to take a quick glance or look. In the context of a "sneak peek," the intended meaning is a quick preview or glimpse, not the top of something.
What is correct?
The correct phrase is "sneak peek".
Examples of correct usage
- The company gave a sneak peek of their new product.
- Fans can't wait for a sneak peek of the upcoming movie.
- Here's a sneak peek at the book's first chapter.