What is the Twilio 21408 Error?
If review request SMS messages are not being delivered to certain customers, you may be encountering a Twilio Error 21408. This error means that permission to send SMS messages to the recipient's country or region has not been enabled in your Twilio account.
This typically affects customers with phone numbers outside of the country your Twilio account was originally set up in.
Common Causes
Geo Permissions not enabled – Twilio restricts outbound messaging to countries not enabled in your account's Messaging Geo Permissions.
Incorrect country code – The customer's phone number may have the wrong international dialing prefix.
Unsupported destination – Some countries are blocked by Twilio due to regulatory restrictions and cannot be enabled.
How to Fix It
Step 1 – Enable the destination country in Twilio
Log in to your Twilio Console
Navigate to Messaging > Settings > Geo Permissions
Find the destination country and toggle it on
Changes take effect immediately — no restart required
Step 2 – Verify the customer's phone number format
Make sure the phone number in Applause includes the correct international country code (e.g., +1 for USA, +44 for UK). An incorrect prefix can trigger this error even if the country is enabled.
Step 3 – Check for country-specific registration requirements
Some countries require additional sender registration before SMS can be delivered. Review Twilio's documentation for the specific country's requirements before enabling it.
⚠️ Note: Certain countries cannot be enabled regardless of settings. Twilio has permanently blocked messaging to Iran, Syria, and Cuba due to regulatory restrictions. If your customer is in one of these countries, SMS delivery is not possible through Twilio.
Need Help?
If you've enabled the country in Twilio and are still seeing this error, reach out to the Applause Support team and provide the customer's phone number (with country code) so we can help investigate further.