The URI urn:ietf:wg:oauth:2.0:oob
is a special URI used to identify out-of-browser applications, i.e. non-web applications (desktop, mobile, command line, etc.).
When you create the credentials in the APIs Console, make sure you select “Installed Application” as the application type and the redirect URI will automatically be set as urn:ietf:wg:oauth:2.0:oob
and prevent the “redirect_uri_mismatch” when making a request.