321403: Invalid grant_type

Twilio could not process the token request because the grant_type parameter is missing or contains an unsupported value. For Client Credentials authentication, set grant_type to client_credentials.

• The request does not include the grant_type parameter.
• The request includes a grant_type value other than client_credentials.
• The request body is malformed, so Twilio cannot read the grant_type parameter.
• The application is using a different OAuth flow than the endpoint supports.

• Include the grant_type parameter in the token request body.
• Set grant_type to client_credentials.
• Send the request using the expected content type and body format for the token endpoint.
• Review your IAM authentication flow and confirm that your application is using Client Credentials where required.

• IAM documentation
• Authenticate with Twilio APIs