What happens after the customer updates their payment details?

If the customer updates their card on file to a new one, the system will charge them again if their status is still "active".

If their status is "failed" that means they've reached the max amount of billing attemps (which is typically defaulted to 3x)

Ongoing defaults to 3 billing attempts for failed payments. This means will try 3x to recapture the payment for a subscription after a card has been declined. The merchant can set the Maximum number of billing attempts of retries by going to Ongoing Settings --> Billing Attempts (here you can see how many times it's set to)

TIP #1 If the customer's subscription status is "Active"

If you want to ensure that your customer will be charged, you can change the next billing date to tomorrow.

From Ongoing --> Subscriptions --> click subscription # --> click Next Billing Date --> seelect tomorrow --> click Save Changes.

TIP #2 If the customer's subscription status is "Failed"

If the customer has a status of Failed you can click Activate Subscription to trigger new billing attempts.

From Ongoing --> Subscriptions --> click subscription # --> click "Activate Subscription"