My company has an Email Plus account on Contact Contact.
We need to use Constant Contact API v3. I have followed the steps given in this article (https://v3.developer.constantcontact.com/api_guide/getting_started.html?_ga=2.29322108.1308822313.16... ) to register my application.
Now, inside my PHP project, when I use the API Key and Secret (Generated through the steps given in the above article), I always get the "Unauthenticated error".
I have tried to make calls to API with api_key as a query parameter and passing the access token in the header and also making a call to API without api_key as a query parameter.