Is it me or the math in the article doesn't make sense. The author is accumulating the costs for selling a SINGLE instance of the product on Shopify, Ebay, Amaz

Is it me or the math in the article doesn't make sense. The author is accumulating the costs for selling a SINGLE instance of the product on Shopify, Ebay, Amazon, and Walmart. When in reality, you would be paying only for the one you sold your product through, even if you offer your product on multiple platforms.