While recently thinking about a scene from the Clone Wars series where Anakin (and possibly Asoka) were paying for something with a number of physical credits, it dawned on me that I have never seen anyone pay with a credit or debit card in Star Wars. So, do credit or debit cards exist in Star Wars?
Yes, there was something of this sort
Watto: How are you going to pay for all this?
Qui-Gon Jinn: I have twenty thousand Republic dataries.
Watto: Republic credits? Republic credits are no good out here. I need something more real.
Qui-Gon Jinn: I don't have anything else
Qui-Gon Jinn: but credits will do fine.
Watto: No, they won't-a.
Qui-Gon Jinn: Credits will do fine.
Watto: No, they won't-a. What? You think you're some kind of Jedi, waving your hand around like that? I'm a Toydarian, mind tricks don't work on me. Only money. No money, no parts, no deal!
So, we see from the very first hand canon that they have a different payment method than cash.
According to Wookieepedia, credit stick is mentioned in several fan fictions along with some Clone Wars episodes and in some relatively canon games like Star Wars: Knights of the Old Republic.
I assume it works as follows:
An unbreakable and untamperable device, equivalent of POS machines is rented/purchased from a bank by the shop owner.
This device reads the credit on paying stick and updates it. After this, it updates the receiving stick as well.
The shop owner can withdraw the money using his credit stick from a bank branch or ATM.
However, this operation describes both the debit card and credit card. I guess if the balance on the credit stick is allowed to go down to a negative number, it acts more like a credit card.
There is no need for real-time communication for credit cards
Touch memory technology allows transfer for money without the need of any communication. It is basically a reprogrammable RFID.
Without high-speed, high-bandwidth interstellar communication to check the balance in real time, issuing credit cards would have to rely on the credit rating of the individual.
The characters we follow in Star Wars are interstellar travelers or living on relatively primitive worlds. Many also have a questionable credit history. Hence loan sharks, who follow the debtor and break kneecaps to collect the debt.