Clinic administrators occasionally report that SMS messages fail to deliver to international phone numbers, or receive errors such as Error 30024 (Numeric Sender ID Not Provisioned on Carrier).
These failures are typically caused by country-specific carrier restrictions on international long codes or improperly formatted phone numbers.
What is an international long code? A long code is a standard full-length phone number (e.g. the US number +12563803216 used in our Twilio account). It is "international" when used to send messages to a different country — for example, sending from a US number to a UK recipient.
Why do carriers restrict them? Mobile carriers classify SMS broadly as either Person-to-Person (P2P) or Application-to-Person (A2P). P2P is two individuals texting each other; A2P is a business or application sending automated messages (appointment reminders, consent notifications, etc.). International long codes were originally designed for P2P traffic. When businesses use them for A2P messaging at scale — which is what FertilityConsent does — carriers treat this as an abuse of P2P routes. To protect their networks from spam and fraud, carriers in many countries now block or filter A2P messages that arrive via international long codes entirely.
How this affects us in practice: The UK is the most relevant example. Since 30 July 2024, all UK carriers block SMS sent from international long codes, regardless of content. A message sent from our US Twilio number (+12563803216) to a UK patient number (+44...) will never be delivered — it is silently blocked at the carrier level with no error returned to the patient. The same pattern applies in other countries at different thresholds and timelines. The solution in each case is to use a sender type that carriers recognise as legitimate A2P traffic: an Alphanumeric Sender ID, a local long code in the destination country, or a short code.