SSJS HTTP.Post ValidEmail with requested Access Token

Question

I am trying to make an API request in SFMC to validate email addresses, which requires first to get the Access Token.

I was able to request the access token, but then the next HTTP.Post request I do doesn't work. I have this far:

Platform.Load("core","1.1.5");


var dataRows = Platform.Function.LookupRows('NameofEmailsDE','ColumnName2Check','ValueName');
 if(dataRows && dataRows.length > 0) {
      for(var i=0; i<dataRows.length; i++) {

        var EmailAddress = dataRows[i]["ColumnNameToRetrieve"];

try {
        var authEndpoint = "https://uniqueclienturlapi.auth.marketingcloudapis.com";
        var client_id = "XXXXXXXXXXX";
        var client_secret = "XXXXXXXXXXX";
        var account_id = "XXXXXXXXX";
        var grant_type = "client_credentials";

        // auth        
        var url = authEndpoint + '/v2/token';
        var contentType = 'application/json';
        var payload = '{"grant_type":"' + grant_type + '",';
        payload += '"client_id":"' + client_id + '",';
        payload += '"client_secret":"' + client_secret + '"}';

        // create token
        var accessTokenResult = HTTP.Post(url, contentType, payload);
        var statusCode = result["StatusCode"];
        var response = accessTokenResult["Response"][0];
        var access_token = Platform.Function.ParseJSON(response).access_token; 



 /* Until here, the request works, and I get the access_token. The issue comes in this next request when I have to add to the HTTP.Post the headerNames + headerValues */



        var restEndpoint = "https://uniqueclienturlapi.rest.marketingcloudapis.com";
        restEndpoint += "/address/v1/validateEmail";  
        var headerNames = ["Authorization"];
        var headerValues = ["Bearer " + access_token]; 

        // payload
          var restpayload = '{';
          restpayload += ' "email": "' + EmailAddress + '",'; 
          restpayload += ' "validators": [ "SyntaxValidator", "MXValidator", "ListDetectiveValidator" ]';
          restpayload += '}';                            

        try {
            var restresult = HTTP.Post(restEndpoint, contentType, restpayload, headerNames, headerValues);
            var reststatusCode = result["StatusCode"];
            var response = restresult["Response"][0];
            var emailresponse = Platform.Function.ParseJSON(response).email;
            var validresponse = Platform.Function.ParseJSON(response).valid;
            var failedValidationresponse = Platform.Function.ParseJSON(response).failedValidation;
            }
        catch (err)  {
            // error
            //Write("error");
            }             
    }           

  catch (err)  {
    // error
    //Write("error");
    } 
  }     
}   

---

I would appreciate any help! Thanks a lot