Build the URL as a string, output it to console and verify is correct, i.e. works in a browser or with curl or similar.
See my app below for WUnderground.
var tag = <#Temperature sensor_[12|13|21|26|32|52|62|72]_1#>;
tag.updated = function () {
function pad(number) {
if (number < 10) {
return "0" + number;
}
return number;
}
var now = new Date();
var wuDateString = now.getUTCFullYear() + "-" + pad(now.getUTCMonth() + 1) + "-" + pad(now.getUTCDate()) + "+" + pad(now.getUTCHours()) + "%3A" + pad(now.getUTCMinutes()) + "%3A" + pad(now.getUTCSeconds());
var humidity = Number(tag.moisture);
var temperatureC = Number(tag.temperature);
var temperatureF = Number(temperatureC) * 1.8 + 32;
var dewPointF = 243.04 * (Math.log(humidity / 100) + (Number(17.625 * temperatureF) / Number(243.04 + temperatureF))) / Number(17.625 - Math.log(humidity / 100) - (Number(17.625 * temperatureF) / Number(243.04 + temperatureF)));
var solarradiation = Number(tag.lux) * 0.0079;
KumoApp.Log(url, 0);
KumoApp.httpCallExternal(url, "GET");
};