Oauth2 Blank Screen when Authorizing API

We have been trying to connect to the API through using the OAuth2 Authorization Code in Insomnia.

We are using:

https://authz.constantcontact.com/oauth2/default/v1/authorize

Parameters:

client_id: ********(It's correct)

redirect_uri: https://localhost

response_type: code

state: {FL}

It gives me the 200 OK with a white screen and nothing else. I'm not sure what we are doing wrong.