Google Apps Script redirects Google Sites gadget

I am building a web application on Google sites. I currently have two forms in a google script, the first loads the table and displays it as a table, and then when you select a row from the table, the script calls another web application with a GET request and with several parameters (like? RowIndex = X & columnIndex = ..).

This works fine if I use the first form as a web application. But if I insert the first script as the “Google Apps script Gadget” on my google websites page, it seems to be embedded in an IFrame that cannot be redirected to other web pages / scripts (it just shows an empty iframe).

Is there any way to solve this without merging both scripts in one?

for redirection I use javascript in html form.

windows.location="secondScriptUrl"+"?parameters..." 

and the second script just generates html from the doGet () function

function doGet(e) {
   return HtmlService.createTemplateFromFile('index').evaluate();
}