What happens if a customer is in dunning and they update their card?
The customer should be charged immediately.
How can I tell if a customer canceled or if their account was canceled due to dunning?
The cancellation_message for customers who are canceled for non-payment is “Canceled after failed automatic dunning process expired.”
It is also worth noting that customers who are canceled after dunning may have a valid card that simply didn’t have sufficient funds/credit to process the payment.
What happens when a subscription’s current billing cycle ends while they’re still in dunning?
The subscription will still attempt to renew, even if a dunning step isn’t defined on the day that the billing cycle ends.