From a transactional account, you can send only those messages that match one of your pre-approved templates. Please ensure that your messages match one of the approved template formats.
If you would like to add a new template to suit your SMS content, log in to your account, select ‘Messaging -> Manage Templates ’ and submit it for review. Once your template is approved, you can start sending messages based on that template.
If the error still persists, please contact support@mobtexting.com.