If you attempt to charge the exact same amount to the exact same credit card twice in one day, the second attempt is likely to be rejected as a "duplicate transaction error." This is a safety feature built in to the charge card system and meant to prevent you from inadvertently charging twice for the same service.
On occasion, however, a duplicate charge is appropriate. You may see two family members on the same day for different sessions, for example.
There is a simple trick you may use to avoid the duplicate transaction error. Simply charge one penny less on the second charge! This amount is small enough to avoid triggering an error in our accounting system, and is not going to hurt your pocketbook substantially.