Oxford Dictionary API Fetch Request ERROR: Authentication parameters missing

I am trying to access dictionary api from chrome console, but constantly getting this error: Authentication parameters missing status code: 403

My credentials have no issue, coz it works fine in postman.

Documentation for oxford dictionary api : https://developer.oxforddictionaries.com/documentation#!/Entries/get_entries_source_lang_word_id

Following is my fetch request:

var myHeaders = new Headers();
myHeaders.append("app_id", app_id);
myHeaders.append("app_key", app_key);

var requestOptions = {
  method: 'GET',
  headers: myHeaders,
  mode : "no-cors",
  redirect: 'follow'
};

fetch("https://od-api.oxforddictionaries.com/api/v2/entries/en-us/persistent?strictMatch=false", requestOptions)
  .then(response => response.text())
  .then(result => console.log(result))
  .catch(error => console.log('error', error));