What you tried was incorrect. The JWT token is not an access token, but it is a user credential that you can use to get the access token and refresh token instead of using the user username and password. If you understand PHP, you can convert this function to VBA script for your app.

private function authenticate(){

      $url = $_ENV["RC_SERVER_URL"] . "/restapi/oauth/token";

      $basic = $_ENV["RC_CLIENT_ID"] .":". $_ENV["RC_CLIENT_SECRET"];

      $headers = array (

              'Content-Type: application/x-www-form-urlencoded; charset=UTF-8',

              'Accept: application/json',

              'Authorization: Basic '.base64_encode($basic)

            );

      $body = http_build_query(array (

              'grant_type' => 'urn:ietf:params:oauth:grant-type:jwt-bearer',

              'assertion' => $_ENV["JWT_TOKEN"]

            ));

      try {

        $ch = curl_init($url);

        curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);

        curl_setopt($ch, CURLOPT_POST, TRUE);

        curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);

        curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);

        curl_setopt($ch, CURLOPT_TIMEOUT, 600);

        curl_setopt($ch, CURLOPT_POSTFIELDS, $body);



        $strResponse = curl_exec($ch);

        $curlErrno = curl_errno($ch);

        if ($curlErrno) {

          throw new Exception($curlErrno);

        } else {

          $httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);

          curl_close($ch);

          if ($httpCode == 200) {

            $date = new DateTime();

            $jsonObj = json_decode($strResponse);

            $tokensObj = array(

              "tokens" => $jsonObj,

              "timestamp" => $date->getTimestamp()

            );

            // Logged in successfully => Save tokens in session or write to file/database for reuse

            $_SESSION['sessionAccessToken'] =  json_encode($tokensObj, JSON_PRETTY_PRINT);

            return;

          }else{

            throw new Exception($strResponse);

          }

        }

      } catch (Exception $e) {

        throw $e;

      }

    }

You can get the entire PHP project from my GitHub repo to learn more about how to use the refresh token to get a new access token if it expires.