Processing credit cards is handled entirely by Stripe's system. The error that is displayed in Teachworks when a declined transaction occurs on the credit card fields is exactly as it is displayed in Stripe.
You can check your Stripe account and view the logs for additional details about the reason the transaction was declined. You can follow the steps below to view a transaction:
Login to your Stripe Account
Click on "Developers", located in the top right of the page
Click on "Logs" on the left hand side
Look for a "402" error that occurred around the time you processed the credit card
Click on the record
The "Response Body" section will contain the details of the error that occurred. You'll be able to see the error code, the decline code and the error message.