Can you define what you mean by "gross margins in the following sentence? "Meanwhile card network operators like Mastercard and Visa extract gross profit margins of as much as 80% through their control of the payment rails."

I found this definition but it does not seem to make sense relative to credit card networks.

Gross margin is the difference between revenue and cost of goods sold (COGS), divided by revenue. Gross margin is expressed as a percentage. Generally, it is calculated as the selling price of an item, less the cost of goods sold (e. g. production or acquisition costs, not including indirect fixed costs like office expenses, rent, or administrative costs), then divided by the same selling price.

Or put differently 80% does not seem excessive since most of the credit card company's costs are indirect fixed costs which are not counted in the calculation of gross margin.