Of course, there are other correct alternatives in Japanese. That is not my point. The article makes two statements that are not correct: 1. "koin ikko ireru

Of course, there are other correct alternatives in Japanese. That is not my point. The article makes two statements that are not correct: 1. "koin ikko ireru" is wrong because of the verb conjugation. The reason it is wrong is that "ikko" is something kids say to each other, or that parents say to their kids, and is weird/incorrect to say in a context where teens and adults are involved. It is also missing the "o" (or "wo," if you prefer). 2. "koin o ireru" is incorrect, again because of verb conjugation. There is nothing wrong with this phrase. Of course, you could say コインを入れてください, コインを一つ入れる, コインを一枚入れる, コインを入れる, Insert Coin, and other variations on that theme. My only point is that the two asserts above are incorrect in the article.