It's an idiomatic error.
People often hear "toe the line" and mistakenly assume it is "tow the line" due to the sound-alike nature of the words "toe" and "tow," and a misunderstanding of the expression's origins.
The correct idiom is "toe the line," which means to conform to a rule or standard. The phrase originates from the idea of lining up with one's toes on a starting line, ready to follow orders or begin an activity.
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