Uncaught SoapFault exception thrown when trying to make request to NOAA's NDFDgen function

Question

I have gleaned from the internet that I should be able to request forecast data using the following PHP:

$wsdl = "http://graphical.weather.gov/xml/SOAP_server/ndfdXMLserver.php?wsdl";
$params = array(
        "latitude" => 43.4685,
        "longitude" => 89.7415,
        "product" => "glance",
        "startTime" => "",
        "endTime" => "",
        "Unit" => "e",
        "weatherParameters" => array(
            "maxt" => TRUE
            )
);
$client = new SoapClient($wsdl);

$result = $client->NDFDgen($params);

However, I am receiving the server error: "Uncaught SoapFault exception: [SERVER] product needs to be either time-series or glance..."

I am providing the param "glance" as a string above, so I don't know what I'm doing wrong. Docs on the NDFDgen function are provided as a table here. Please help me if anyone can spot my error. Thanks!