Error: Request Security Violation at /oauth/v2/token

Hi,

I am trying to get an access Token through the API. I follow this guide:

How to create Access Token Using Postman (adobe.com)

With the use of the following page and other resources on the Internet, I made a small python script for the request to the redirect uri:

What’s needed on the “redirect URI” page? (evernote.com)

In Postman I get to point 13 in the guide, where the window says authentication complete, but the following window that should show the token just shows some gibberish.
I looked into the body of the last response in Postman, which was following the request to https://secure.eu2.adobesign.com/public/userMessage.
When I copy and paste the contents into an html file and open it in the browser, it prints above message:
"Error: Request Security Violation at /oauth/v2/token"

I have been altering the python script several times to check for some points that I could have misunderstood or I wasn't sure how to interpret, but nothing happens.

More over it seems that there has never gone a POST request to the redirect URL, I could not fetch and log any requests with my python script. My python is rusty though, but sending a post request from postman to it it will be logged.

I tried with

https://<redirectUrl>?code=<code>&state=<state>

I got the link from the response header "Location" in the POST request to

https://secure.eu2.adobesign.com/public/oauth/v2

from the Postman console.

Any help appreciated.