To change from using one-way SMS reminders (that do not allow patients to respond) to two-way SMS reminders:
Click Settings > Reminders.
In the Preferences section, click the Edit (pencil) icon.
Tick the checkbox labelled "SMS two way reminder".
At the bottom of the pop-up, tick that you want to apply the change to all future appointments.
You should also update your reminder wording:
In the Copy section, click the Edit (pencil) icon next to Pre-appointment Reminder.
In the SMS/Text Copy field, remove any wording that says 'Please do not reply to this message'.
In the 2-way Copy field, review the wording that is appended to the SMS/Text Copy. By default, the wording says, "Reply YES to confirm or call [your phone number] to reschedule".
You are now set up for two-way reminders.