When the payment fails in the payment plugin, it saves the order as waiting for payment. If the payment is unsuccessful, I don't want to save the order and I want the cart to stay the same. How can I do that?

Hello, Alp.

Please look at the Braintree plugin which is available out of the box in GrandNode. It should give you some thoughts in which direction you should go. If not, it's also possible to make a custom redirect payment method that will fulfil your scenario. However, it requires more work. You can reach us at support@grandnode.com and we can make a custom development for you.