title: errore with messageSignature sha256 in postman (base64 is notdefined.)
body: <p>I'm testing an api that i have to send in body those data acording to documentation:</p>
  <pre><code>studentId,
  apiKey,
  timeStamp (current iso time as a string),
  messageSignature: apikey+studentId+timeStamp encrypted using sha256,
  </code></pre>
  <p>i wrote a script to generate message signature  using sha256 in Pre-request Script.
  Pre-request Script:</p>
  <pre class="lang-js prettyprint-override"><code>
      var dateIso = new Date().toISOString();
      pm.globals.set(&quot;isoDateTostring&quot;, dateIso);
      console.log('timestamp var is:', pm.globals.get(&quot;isoDateTostring&quot;));
      
      let msg = &quot;apiKeyvalue&quot; + &quot;studentId&quot; + pm.globals.get(&quot;isoDateTostring&quot;);+ JSON.stringify(msg)
      
      const hmac = CryptoJS.algo.HMAC.create(CryptoJS.algo.SHA256, &quot;secretKey&quot;);
      hmac.update(msg);
      const messageSignature = hmac.finalize().toString();
  
  </code></pre>
  <p><em>Details (like screenshots)</em>:
  in body i wrote:</p>
  <pre><code>{
  &quot;studentId&quot;:&quot;********&quot;,
  &quot;apiKey&quot;:&quot;************&quot;,
  &quot;timeStamp&quot;:{{$isoDateTostring}},
  &quot;messageSignature&quot;: {{$messageSignature}}
  }
  </code></pre>
  <p>when i send the request i get base64 is notdefined.</p>
  <p></p>
  <p><a href="https://i.stack.imgur.com/bRKQO.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bRKQO.png" alt="enter image description here" /></a></p>