Over the weekend, we deployed a minor update to our credit card processing. The update passed QA, but once in production, the new code triggered an unexpected error condition at Stripe (Kickserv's credit card processor). This caused some credit card payments to fail with an error message. We rolled back the update Monday morning and all payments since have processed without issues.
If you or your customers processed a credit card payment over the weekend (from May 19 to the morning of May 22), check to make sure those payments went through, and run them again if necessary. We're sorry for the inconvenience.