https://www.vocabulary.com/articles/pardon-the-expression/toe-the-line-vs-tow-the-line/

“toe the line” vs. “tow the line”

On your mark, get set, go! When you stand ready for a race with your toes on the starting line, you literally toe the line.

In fact, people used to say, “Toe your mark, get set, go!” These days, the expression toe the line is more commonly used to refer to doing what’s expected of you, or conforming. If you constantly misbehave in class, your teacher might tell you that you need to start toeing the line.

This phrase can also mean being right up against the line between two different things. If your short story toes the line between fantasy and science fiction, then it probably includes elements of both those genres but doesn’t neatly align with either one. Any way you use it, the idiom toe the line always uses toe as in the one at the end of your foot.