Sandbox (Testing): https://gateway.sand.us.zip.co/orders/calculate-merchant-fees

Merchants with a merchant fee for payment plan (i.e. MFPP) agreement can use this endpoint to determine the fee amount for a given order. The state/country for the customer should come from the customer's billing address (use shipping address if no customer billing address is collected). When $0 is returned, then there is no fee and does not need to display within the merchant's UX.