Yes.

First, if you don't have one, set up a Subtotal type item.

Then, set up an other charge where the price is 4%.

On the invoice, add the subtotal and then add the other charge item and it'll calculate 4% of the amount above it.

Before you do this, though, make sure you follow the rules. For example, you have to "register the surcharge with the payment network." ahead of time.

Also, you cannot charge the customer more than you pay in fees for the transaction, which means you have to know how much you're going to pay based on the card type (standard, rewards, business, international and other sub-types often have different fees), or know how much cheapest fees are and charge that amount, which is probably less than 4%.

See

https://usa.visa.com/support/small-business/regulations-fees.html and

https://usa.visa.com/content/dam/VCOM/global/support-legal/documents/merchant-surcharging-qa-for-web...