Handling Twilio REST API Error Codes and Implementing Retry Logic – Twilio Support

Overview

When integrating with Twilio’s REST APIs, it’s important to handle errors gracefully to ensure your application is robust, efficient, and resilient to transient issues. This article explains how to distinguish between retryable (transient) and non-retryable (terminal) errors, and provides guidance on implementing effective retry logic.

Why Use HTTP Status Codes for Retry Logic?

Twilio REST API responses include both HTTP status codes and Twilio-specific error codes. Because Twilio may introduce new error codes over time, it is more maintainable and future-proof to base your retry logic on HTTP status codes rather than enumerating every possible error code.

What You Need To Know

Retryable vs. Non-Retryable HTTP Status Codes

Retryable (Transient) Status Codes

These status codes indicate temporary issues that may resolve on their own. It is generally safe to retry requests that return these codes:

HTTP Status	Meaning	Notes
429	Too Many Requests	Rate limiting; respect `Retry-After` header
500	Internal Server Error
502	Bad Gateway
503	Service Unavailable
504	Gateway Timeout

Non-Retryable (Terminal) Status Codes

These status codes indicate permanent issues that will not be resolved by retrying. These require code or configuration changes:

HTTP Status	Meaning	Typical Cause
400	Bad Request	Invalid parameters
401	Unauthorized	Authentication failure
403	Forbidden	Permission denied
404	Not Found	Resource does not exist
405	Method Not Allowed
422	Unprocessable Entity	Validation errors

Recommended Retry Strategy

Exponential Backoff: For retryable errors, use exponential backoff (e.g., wait 1s, then 2s, then 4s, etc.) up to a reasonable maximum.
Maximum Retries: Set a maximum number of retries (commonly 3–5 attempts).
429 Handling: For HTTP 429, always respect the Retry-After header if present.
No Retries for 4xx (except 429): Avoid retrying for non-retryable status codes, as these indicate issues that must be fixed in your request or configuration.

Example Logic

if response.status_code in [429, 500, 502, 503, 504]:
    # Retry with exponential backoff
elif response.status_code in [400, 401, 403, 404, 405, 422]:
    # Do not retry; investigate and fix the request
else:
    # Handle other status codes as appropriate

Conclusion

Use HTTP status codes to determine retry logic for Twilio REST API errors.
Retry only on transient errors (429, 500, 502, 503, 504) with exponential backoff and a maximum retry count.
Do not retry on permanent errors (400, 401, 403, 404, 405, 422); these require code or configuration changes.
Always respect the Retry-After header for rate limiting.

By following these best practices, you can build more reliable and efficient integrations with Twilio’s APIs.

Below you will find references to useful documents:

If you have further questions or need clarification on specific error codes or scenarios, please refer to the resources above or reach out to Twilio Support.