In a credit card fails and needs to be updated by the customer what flag is set or where what is the simplest way to determine that a user has outdated CC information?

This would probably be different from one payment method to another, but you would need to look at the payment record itself and based on that determine if the source is bad or not. There are many reasons why a payment could fail and not all mean the customer needs to change their payment source, but that’s probably a business decision based on what the gateway response was. Sometimes it’s just sufficient to retry the payment at a later date (like in the case of NSF).

Got it

No problem! I hope this is helpful, I know some payment providers like Stripe have a way to send you a webhook when a customer updates their card because sometimes even expired cards can be charged successfully if the customer just renewed it, however I’ve never implemented anything like that. The scenario I’ve had to deal with is implementing a retry schedule based on the type of failure.

Got it.. yes I sorta wish that was taken care of but I certainly can understand it being application specific.