When two-way SMS reminders are sent to patients, you can see their response in your calendar. If the response does not fit the standard yes/no (or Y/N) format, a message is displayed saying "Check Response", which tells you to look at the message.
You can do this by clicking the amber colour on the appointment and then clicking the bell icon to view the Reminder History. You can see the response when you hover the mouse over the magnifying glass icon.
Please see the following for more information on two-way SMS response colours.