Send email via javascript with email body containing data from text input box in Captivate 9?

I have written some code that is activated upon the clicking of a 'submit' button through Execute Javascript. The window.cpAPIInterface.getVariableValue function does not seem to be working. The text entry box has a variable value 'Feedback_Input_Text'. What am I doing wrong? The basic email is sending, with just a normal piece of text, and with: var InputText = "Some Text". But I cannot extract the text entry text. Please help. Thanks!

function log(obj) {

    $('#response').text(JSON.stringify(obj));

}

var m = new mandrill.Mandrill("fG8zVp0HdF_oPuCoa2uYvg");

var InputText = window.cpAPIInterface.getVariableValue("Feedback_Input_Text");

var params = {

    "message": {

        "from_email":"alastair@trnsys.guru",

        "to":[{"email":"alastair.mcdowell@energyae.com"}],

        "subject": "User Feedback",

        "text": InputText

    }

};

function sendTheMail() {

    m.messages.send(params, function(res) {

        log(res);

    }, function(err) {

        log(err);

    });

}