# 40142: Token expired

Identifier: `token_expired`



The client's connection or request was rejected because the authentication token had expired. Each token has an expiry time that is set when it is issued.

## What you should do

Usually nothing. Token expiry is a normal part of token authentication, and a client configured to renew its own tokens recovers without any intervention: it requests a fresh token and continues. A 40142 that appears briefly and then clears is expected, not a fault.

You only need to act when the error persists or surfaces to your application. That means renewal isn't happening — a configuration or auth-endpoint problem rather than the expiry itself, covered below.

## Why it happens

When 40142 reaches your application instead of being handled silently, the cause is usually one of the following.

- No renewal mechanism is configured. Without `authUrl` or `authCallback`, the SDK has no way to obtain a replacement when a token expires. [Configure one of these](https://ably.com/docs/auth/token.md) so renewal happens automatically.
- The auth endpoint is unreachable or slow. If the `authUrl` or `authCallback` fails or times out when the SDK tries to renew, the expired token is all that remains. Check that your token-issuing endpoint is reachable and returns a valid token promptly.
- The token was issued with a very short lifetime. A small `ttl` causes tokens to expire sooner than expected, sometimes before the SDK renews them. Review the `ttl` you request against how long your clients actually need it.
- The client clock is significantly skewed. A token can appear expired immediately after issue if the client's clock differs substantially from real time. Ensure the client clock is reasonably accurate.

## What you'll see

The error is reported with code 40142 and HTTP status 401. The message is typically `Token expired`; some server paths report `Access token expired`.