When reviewing SMS (text message) receipts for a sent message, the Omnilert system will show successes (Accepted by Carrier, Delivered to Handset, etc) as well as any texts that were rejected.
These receipts are returned by the recipient's mobile carrier and thus are often somewhat cryptic. For obvious privacy reasons, a phone carrier cannot expose an individual's account info, payment info, or anything else of a personal nature.
They can tell whether the text was accepted or rejected.
A common rejection error we see is Carrier Unavailable.
This typically indicates that the subscriber's mobile service plan is blocked or restricted from receiving short code text messages.
Shortcodes are short format phone numbers used by services like Omnilert to send mass texts.
Omnilert sends SMS from the shortcode 79516.
What can you do?
Ask the owner of the device to text the word HELP to 79516. They will likely receive a response from their carrier indicating that the message was blocked. (e.g. "Service Access Denied", "Short Code Blocked or Expired", "Rejected", etc.)
That error message should be helpful to their carrier's support to help them unblock texts. Some are rather cryptic.
As you may guess, the end-user is going to need to call their phone carrier support for assistance as this problem stems from their account with their provider. They will want to ask their carrier to allow 79516 to send texts to their phone.
If nothing else works...
Alternatively, the end-user could try selecting "Other" as their carrier. The "Other" carrier setting sends via a random 10-digit long code and can sometimes work for users who otherwise cannot receive shortcode SMS.