When sending a message to a large list, it's common to have a few failed numbers. Most text messaging providers don't show this data, but we feel it's more transparent to show it, instead of just showing # of delivered messages and opt-outs.
The common reasons for failed numbers:
Mobile number has been deactivated by their wireless carrier
Landline number (typically from a 3rd-party integration like your ChMS or an imported file)
Mobile number has Shortcode messaging blocked with their wireless carrier (if you've created a Longcode to use as a fallback, you won't have to worry about this). Sometimes people have Shortcode messaging blocked with their wireless plan (often beknownst to them). The best way to ensure the highest success rate for you messages is to use a Shortcode, but create a Longcode to use as a fallback for those who cannot receive Shortcode messages.
You're not charged any message credits for these failed messages, and if you ever need to know which numbers failed, just reach out to our support team.