This article will list many common reasons for SMS failure or no SMS messages being sent. 

1. Message bodies are longer than 1600 characters. Sending lengthy SMS messages can stall your message queue for hours and eventually the SMS gateway will block your message. 

2. If you have entered in your personal number under Business Setup, SMS gateways will block your message due to laws against terror, anti-spoofing and money laundering.

3. An incorrect or disconnected number! Simply confirm with a patient that you have the correct mobile number for them.

4. The "SMS Identity" that you are using is incorrect. To check, click on the Business Setup -> Email & SMS Identity settings, and check that the "Default SMS Number" contains ONLY alphanumeric characters, and no symbols like hyphens or spaces.