# 51007: Client Connection: Token authentication is rejected

Log Type: APPLICATION

Log Level: ERROR

## Description

### Possible causes

Authentication service has rejected provided Access Token.

To check whether the Access Token is structurally correct, you can use the tools available at [jwt.io](https://jwt.io/).

For the details of Twilio's specific Access Token implementation including the grant format, see [the documentation](/docs/iam/access-tokens).

### Possible solutions

For further assistance, please reach out to Twilio Support through the [Console](https://console.twilio.com) or [Help Center](https://support.twilio.com).