The failure message is stored on the subscription and shown at the top of its page as "Last auto renew error: ..."; the plan name turns red in the list with the error as a tooltip. The customer receives the Subscription: Renew Error notification and your business email receives Admin: Subscription Renew Error. While the subscription is still inside its renewal window it is not flagged as an error, so the next scheduled run simply retries. Once the renewal date has passed without success, the subscription is flagged Error = Yes: it is excluded from further automatic retries, counted in Total Errors, listed on the Subscriptions Errors page, and the Dashboard shows "Auto renew encountered N subscriptions with errors".