SMS Shows 'Sent' Status but Not Delivered to Recipient's Handset

What's happening?

An SMS message sent to a customer shows a status of 'Sent' but does not reach the recipient's device, and thus does not show a 'Delivered' status.

Reason:

The SMS channel was configured using an Australian number, which is not supported for configuring SMS delivery. Currently, SMS is only available for US, Canada, and Puerto Rico. 

Resolution:

Ensure that the SMS channel is configured using a supported number. 

See Country/regional availability of telephone numbers and subscription eligibility - An Azure Communication Services concept document | Microsoft Learn for information