Google Ads API with Google Apps Script no access token received

I am trying to use Google Ads on Google Apps Script using this guide. I created client id and client secret on Google Console's API & Services.

Not too sure if this configuration is correct but the account is linked to Google Apps Script as I have pagespeed insights as well and there are some requests on the dashboard. I added https://www.googleapis.com/auth/drive as the scope. Again not too sure if I should add Google Ads to the scope. Lastly, got my refresh token from Google Auth playground. When I run the script above I got the following error:

Error: No access token received: {   "error": "invalid_client",   "error_description": "Unauthorized" } authenticate_   @ test.gs:120 withRefreshToken    @ test.gs:144 initializeOAuthClient   @ test.gs:28 

Honestly not too sure what I am doing wrong here so any help would be very much appreciated. Thank you.

Edit Codes:

//From Google Console API & Services var CLIENT_ID = '"MY_CLIENT_ID'; var CLIENT_SECRET = 'MY_CLIENT_SECRET'; //From Google Authplayground var REFRESH_TOKEN = 'REFRESH_TOKEN'; // Enter scopes which should match scopes in File > Project properties // For this project, e.g.: https://www.googleapis.com/auth/drive var SCOPES = "https://www.googleapis.com/auth/adwords"; // Script ID taken from 'File > Project Properties' var SCRIPT_ID = 'MY_SCRIPT_ID'; var authUrlFetch; // Call this function just once, to initialize the OAuth client. function initializeOAuthClient() {   if (typeof OAuth2 === 'undefined') {     var libUrl = 'https://developers.google.com/google-ads/scripts/docs/examples/oauth20-library';     throw Error('OAuth2 library not found. Please take a copy of the OAuth2 ' +         'library from ' + libUrl + ' and append to the bottom of this script.');   }   var tokenUrl = 'https://accounts.google.com/o/oauth2/token';   authUrlFetch = OAuth2.withRefreshToken(tokenUrl, CLIENT_ID, CLIENT_SECRET,     REFRESH_TOKEN, SCOPES); } /**  * Execute a remote function.  * @param {string} remoteFunctionName The name of the function to execute.  * @param {Object[]} functionParams An array of JSON objects to pass to the  *     remote function.  * @return {?Object} The return value from the function.  */ function executeRemoteFunction(remoteFunctionName, functionParams) {   var apiParams = {     'function': remoteFunctionName,     'parameters': functionParams   };   var httpOptions = {     method: 'POST',     headers: {       'Content-Type': 'application/json'     },     payload: JSON.stringify(apiParams)   };   var url = 'https://script.googleapis.com/v1/scripts/' + SCRIPT_ID + ':run';   var response = authUrlFetch.fetch(url, httpOptions);   var data = JSON.parse(response.getContentText());   // Retrieve the value that has been returned from the execution.   if (data.error) {     throw Error('There was an error: ' + response.getContentText());   }   return data.response.result; } // Paste in OAuth2 library here, from: // https://developers.google.com/google-ads/scripts/docs/examples/oauth20-library 

I have pasted the oauth2.0 library under the codes above.

Edit 2
I fixed the part of function initializeOAuthClient. It now shows execution complete, but when I try to run function executeRemoteFunction I am getting TypeError: Cannot read property 'fetch' of undefined. I am guessing I have to input remoteFunctionName and functionParams but where do I find them?