Why has my request failed with "unauthorized_client"?

An incorrect auth link

Make sure that the Authentication Link you're using is valid for both live and sandbox environments.

Live: https://auth.truelayer.com 

Sandbox: https://auth.truelayer-sandbox.com

An incorrect clientId

Make sure that the clientId that you're using is valid for both live and sandbox environments.

Example Live: truelayersupport-1a2b3c 

Example Sandbox: sandbox-truelayersupport-1a2b3c

You can check this in the TrueLayer Console, under App Settings. 

An incorrect redirect_uri

Make sure that the redirect_uri that you're using is valid.

Example Live: https://console.truelayer.com/redirect-page

Example Sandbox: https://console.truelayer-sandbox.com/redirect-page

Check the URI that you are using is whitelisted in the Console under App Settings.

More

If you need more information...

Have a look at our comprehensive list of the authentication error descriptions in our API documentation.