Due to new security requirements some of the features in Front Desk now require the correct date and time set on your computers. This includes SMS delivery receipts, Automated SMS, Physitrack integration and banking interfaces. This change is required to enhance security and prevent a type of identified security issue call a Replay Attack.
If the time on your system is not correct, Front Desk will notify you via the Messages tab of the Appointment Book. Do not ignore this message as this will prevent these features from working.
If you see this message, at a minimum you should manually set the affected computer to the correct time. To ensure your computer always has the correct time, best practice is to use an automated process with an approved time source as per the following article; How to Synchronize the Clock in Windows 10 with Internet or Atomic Time
For more information on Replay Attacks please see here: https://www.kaspersky.com/resource-center/definitions/replay-attack