Parameters to pass get access token using acquireTokenSilent (MSAL.js)

Hi Guys, 

Newbie here for both Power BI and Javascript. Based on my code below, it seems it gives me an 'access' code but when I use it as a bearer token to get the embed token it throws an 403 forbidden error when I try/simulate it via Postman. However, if I get the access token via Postman I can use the returned access token and use that to get the embed token. 

Programatically:

// Add here scopes for access token to be used 
        const tokenRequest = {
            scopes: ["openid", "user.read"]
        };

        const myMSALObj = new Msal.UserAgentApplication(msalConfig, function (errorDes, token, error, tokenType, instance) {
            // this callback is called after loginRedirect OR acquireTokenRedirect. It's not used with loginPopup,  acquireTokenPopup.
            if (error) {
                console.log(error + ": " + errorDes);
            }
            else
                console.log("Token type = " + tokenType);

        });

        debugger;
        myMSALObj.loginPopup(loginRequest)
            .then((loginResponse) => {
                //Login Success callback code here
                debugger;
                console.log("id_token acquired at: " + new Date().toString());
                console.log(loginResponse);
                myMSALObj.acquireTokenSilent(tokenRequest).then(function (accessTokenResponse) {
                    // Acquire token silent success
                    // Call API with token
                    debugger;
                    let accessToken = accessTokenResponse.accessToken;

Postman (see attachment)