It happens to everyone eventually. For whatever reason, the card you used to pay for your session didn't go through on the site and needs reprocessing. This is a very easy fix.
If you are a GM looking for how to add your bank account for payouts, please check out this FAQ article!
How to Update Your Payment Method:
Go to your "Account Settings" and click on "Payment"
Under "Update Payment Method," enter your new card number, the expiration date, and CVC
Click "Save," and now your card is updated β