I would have let my Tweetbot subscription renew in early February. I guess it was removed from sale, but weirdly Apple shows the wrong error: payment method declined. The payment method is fine (other stuff has gone through since).

Screenshot of App Store subscriptions: Tweetbot for Twitter Tweetbot Yearly Your payment method was declined. To avoid interruptions to your subscriptions and purchases, update your payment method. Update Payment Method Cancel Subscription If you cancel, you will immediately lose access to your subscription.
Douglas Hill @douglas