When is an SMS marked as "Undelivered"?

Sometimes, your message is mark as "Undelivered" because of the following common reasons:

The To number is unknown or no longer in service.
The 'To' number is unreachable - the device is likely powered down, out of the service area, or may not accept your messages.
The destination carrier is filtering out your messages for delivery.
Your message has been blocked from reaching the destination.
The destination is a landline phone, or the destination carrier can't be reached.

Why is undelivered SMS charged?

When a message is sent successfully from our platform but is not received at the end user's handset, we're already charged by the carrier. Therefore, you will be charged for a message if delivery is attempted, i.e., the message status is "sent," "delivered," "undelivered," or "delivery unknown."
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