Good day all, I'm developing a php page in which there is an iframe, that opens another php page with a checkbox in it, this second page, when the user click on the checkbox, has to make an ajax call to confirm the "click".

so there is pageA.php, with a iframe in it that points to pageB.php, in this one, there is only a form with a checkbox and a javascript (vanilla javascript), that sould call a third page on click.

this is the javascript I'm using to send the "click":

document.getElementById("checkboxMe").onclick = function() {
    xhttp.open("POST", "pageC.php", true);
    xhttp.send("foo=bar");  
    };

when clicking on the checkbox, this is what I see on the console:

Uncaught ReferenceError: xhttp is not defined

it never happen something like this, infact I can't find this error easily on google, does anyone has some clues? maybe is the fact I'm into an iframe? how could I solve this issue?

thanks in advance ppl.