What is surcharge?
An extra fee added to a credit card sale to cover the cost of taking the card. It's allowed on credit cards only, never on debit cards.
The card networks cap it and require you to register first, post a notice, and show the fee on its own line of the receipt. Washington allows it within those rules.
For example
A shop adds a 3% fee to a $100 credit card sale, so the customer pays $103. The same sale on a debit card gets no fee.