title: Add header to every request in Postman in pre-request script
body: <p>I want to automatically add a header to every request in my whole collection using this pre-request script:</p>
  
  <pre><code>pm.request.headers.add({
      'key': "myvar",
      'value': pm.environment.get("myvar")    
  });
  </code></pre>
  
  <p><strong>myvar</strong> is an environment variable.</p>
  
  <p>Unfortunately, it doesn't work. Did I miss something?</p>