Basically, Interchange fees are charged by banks for using a credit card. These rates do not change and are included to your processing bill. Credit card processors do not make up interchange rates. VISA, Mastercard, Amex, Discover regulates interchange rates.
An interchange rate is a fee charged by banks that covers the cost of handling and credit risk inherent in a bank credit or debit card transaction. Interchange fees are usually paid to the bank funding a transaction and thus bearing the risk.
source: https://www.investopedia.com/terms/i/interchange-rate.asp
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Interchange Plus Pricing