Authentication Error

Hello,

I am attempting to authenticate by using postman but I am running into an issue. When I run the request, I receive a "200" response, but it is all HTML and does not include an error. Is there something glaring that I am doing wrong? Thanks in advance.

Original GET request: https://authz.constantcontact.com/oauth2/default/v1/authorize?client_id={myclientid}&redirect_uri=https://localhost&response_type=code&state=testvalue