JavaScript Fetch api with credentials and Client_ID (Cornerstone API)

Question

I have a customer that provided these details for a API I need to use:

User_ID: "my_User_ID"
Client Secret: "my_client_secret"
Client_ID: "my_Client_ID",
Registered Oauth application name: Internal Careersite
Access Token Validity Period: 3600
Base adress: https://mySite-pilot.csod.com

Oauth scopes: Cornerstone API, jobrequisition:read  - allows GET requests to following endpoints:            
/services/api/Recruiting/JobRequisitionDetails

I read this guide for the API: https://apiexplorer.csod.com/apiconnectorweb/apiexplorer#/info

I then do a fetch to test my API (proxyUrl is a proxy for no-cors):

fetch(
        proxyUrl +
          "https://mySite-pilot.csod.com/services/api/Recruiting/JobRequisitionDetails",
        {
          headers: {
            "clientId": "my_Client_ID",
            "userId": "my_User_ID",
            "clientSecret":"my_Client_Secret",
            "Content-Type": "application/json",
            "grantType": "client_credentials",
            "scope": "jobrequisition:read",
            'cache-control': 'no-cache',
            Accept: "application/json",
            method: "GET",
          },
        }
      )
      .then((response) =>console.log(response))
      .then((data) => console.log(data));

Above fetch will return a 401 "authorization denied". I do believe that the way I authorize with my credentials is wrong, rather than the information I got. Is there anything wrong with the code?