Why are donors see a "Payment Error: (11) - A duplicate transaction has been submitted." after attempting to submit a donation?

There are circumstances in which a donor might see the following error after attempting to submit a donation through the Donations app.

Payment Error: (11) - A duplicate transaction has been submitted.

This error occurs when a Soapbox Engage account uses Authorize.net as a payment gateway, and Authorize.net believes the transaction to be an exact duplicate of a previous transaction.

Error 11: A duplicate transaction has been submitted. (Authorize.net documentation)

A common situation in which this occurs is when the donor submits a donation that has an incorrect CVV for the credit card, and the donor subsequently submits a second donation attempt with only the CVV changed.  Unfortunately, Authorize.net does not recognize the CVV as a value that if changed would avoid the duplicate transaction trigger.