Error 20003: Authentication Error – No Credentials Provided When Assigning a Flow to a Twilio Number – Twilio Support

Issue

This article addresses the common issue where users encounter error code 20003: Authentication Error – No credentials provided when configuring a Twilio Studio Flow with a Twilio phone number. This typically occurs when the REST API URL is used instead of the required Webhook URL in the phone number’s configuration.

Symptoms

Incoming calls or messages to a Twilio number do not trigger the expected Studio Flow.
Studio Flow execution logs or Twilio error logs show:
- code: 20003
- message: Authentication Error – No credentials provided
- HTTP status: 401

Cause

This error occurs when the REST API URL for the Studio Flow is used in the phone number’s configuration instead of the Webhook URL.

REST API URL: Used for programmatic triggering of Flows via API calls (requires authentication).
Webhook URL: Used to connect a Flow to a Twilio phone number or messaging service (does not require authentication).

Resolution

Identify the Correct Webhook URL for Your Studio Flow
The Webhook URL format is:

https://webhooks.twilio.com/v1/Accounts/{AccountSid}/Flows/{FlowSid}

Replace {AccountSid} with your Twilio Account SID.
Replace {FlowSid} with your Studio Flow SID.

Update Your Twilio Number’s Configuration
- Go to the Active Numbers section in the Twilio Console.
- Select the phone number you want to configure.
- Under the Voice & Fax or Messaging section, set the “A Call Comes In” or “A Message Comes In” webhook to the correct Webhook URL for your Studio Flow.
Save Changes and Test
- Save the configuration.
- Test by calling or messaging the number to confirm the Studio Flow is triggered as expected.

Example

Incorrect (REST API URL):

https://studio.twilio.com/v2/Flows/FWXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/Executions

Correct (Webhook URL):

https://webhooks.twilio.com/v1/Accounts/ACXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/Flows/FWXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

Additional Information

The REST API URL requires authentication and is not suitable for direct assignment to a phone number’s webhook.
Always use the Webhook URL when connecting a Studio Flow to a Twilio number or messaging service.

Below you will find references to useful documents:

This article is intended for Twilio users configuring Studio Flows with phone numbers or messaging services and encountering authentication errors.