FUNCTION_RATE_LIMIT error occurs when the limit of concurrent executions for Serverless Functions has been reached, and the request triggers a new instance of the function, which results in two concurrent functions running at the same time. For more information see What should I do if I receive a 429 error on Vercel?
To troubleshoot this error, follow these steps:
- Check application logs: Review the application logs to identify any specific errors related to the Serverless Function being invoked. For example, your function might be waiting for a slow backend API without a reasonable timeout. They can be found at the host URL under the
- Review deployment configuration: Double-check the deployment configuration to ensure that the Serverless Function is being deployed correctly
- Investigate build errors: If the error occurs during the build process, troubleshoot any build errors that might be preventing the necessary resources from being deployed
- Check function code: Ensure that the code for the Serverless Function is correct and does not contain any errors or infinite loops
- Increase the concurrency limit: If you would like to increase the limit, contact Vercel support