Why have my messages failed to send?

Typically messages will fail to send because either the mobile number of the intended recipient(s) is invalid.

The recommended format for mobile numbers is to include the international prefix (dial code) and no non-numerical characters such as brackets:
- Correct: +61412345678
- Incorrect: (0061) 0412 345 678
If your numbers are all saved in the correct format, then there is a chance that the number itself is invalid/not in use, or that the sender ID (when sending from a number as opposed to an alpha tag) has been blocked by the recipient.
There is also the possibility that the carrier themselves are experiencing issues which could impact your messages being sent successfully.