Why did a customer receive two (or more) reminders?

Under normal circumstances a customer will only receive their reminder SMS once, but there are a couple of exceptions...

• The message was sent once, but received multiple times.
• The message was sent twice, because the appointment was changed to allow this.

Check the SMS Detail Report

The first thing to check is the SMS Detail Report. With this you can determine whether or not the message was sent more than once.

Why would a message that was sent once, be received multiple times!?

Although we sometimes think of an SMS as being instant, this is not quite true.  When an SMS is sent it goes into a queue in the mobile carrier's network.  This is important because it may be that the recipient has their phone turned off or is out of range.

When the phone is switched on and in range, the network delivers the message to the phone.  The phone then must acknowledge that it received the message.

Mobile networks have a policy of "guaranteed delivery", and if they do not receive the acknowledgement they will try sending the message again.

This can happen because the phone drops out of range just as the message is delivered, or for other reasons, and the result is that the message is then received twice.

This is simply the nature of mobile networks, and can happen regardless of whether the message is being sent from another phone, or through an automated service like BizDiary.

Appointment changed to allow reminder to be resent

This is possible, but unlikely to happen accidentally.  For a reminder to be resent, one would have to uncheck the Reminder sent check-box, and change the Status to Unconfirmed.  If you do that BizDiary will think that you want the reminder sent again.  And in fact this is what you SHOULD do if for example you move or copy an appointment (that has already been reminded) to a new time, and which now required a new reminder to be sent.

So, did I have to pay for two messages?

You only pay (in credits) for the messages that are actually sent.  If a message that was sent once gets delivered twice, you only pay once, because it was only sent once.

If the appointment was changed, and the Status and SMS Sent fields were reset, then the message will be sent again, and you will be charged for the new message.