Identity Server 4 : Sorry, there was an error : unauthorized_client

I have set up identity server 4 to extent Umbraco so it uses a custom role provider.

Everything was working but now when I get redirected to my Identity server I get this error:

Can anybody shine some light on this error? I have tried rolling back my code in source control but nothing I do seems to help it. Is there anywhere I can see an error log?

Thanks, Scott