XMLHttpRequest.send() is not sending "UNION SELECT"

Question

I have a JavaScript function that send data to a PHP file and get result from that file
here is my function

function sendForm(formData , url , callBack){
    let form_data = new FormData(document.querySelector(formData));
    let r = new XMLHttpRequest();
    r.open("POST", url , true);
    r.send(form_data);
    r.onreadystatechange = function () {
      if (r.readyState != 4 || r.status != 200)return;
        // this method let us to use result out of function scope 
        if(callBack) callBack(r.responseText);
    };
}

this function get id or classname of a form , url of the page to post data , a callback for further actions
now the problem is if any of my form fields contains this string ("UNION SELECT") nothing happens and i'll get an error (Failed to load resource: the server responded with a status of 403 ()) in (r.send(form_data)) line
please help me ,Thanks

Answer 1

This has nothing to do with your client-side code.

The server is just recognising that string and rejecting it.

This is likely caused by a security feature on the server aggressively defending against SQL Injection attacks. Possibly even this rule.