OAuth, problem with authorization page

I am trying to use OAuth 2 to authenticate my app.

First I registered my application in the Admin Centre under Apps and integrations - OAuth Clients

There I have the following data:
Unique Identifier = mytestclient.
Redirect URLs = https://mytest.srv.no/zendeskRedirect

Then I try to send the user to the Zendesk authorization page using this URL:

https://mysubdomain.zendesk.com/oauth/authorizations/new?response_type=code&redirect_uri=https://mytest.srv.no/zendeskRedirect&clientid=mytestclient&scope=read+write

But the response code is 400 Bad Request
and the text:
Invalid Authorization Request
No such client

Am I missing something here?