Ajax请求错误的URL

Question

I have page url/index.php which has a ajax request in it for url/submit.php. On most computers it works fine, but I have a client who's computer request url header is from url/index.php/submit.php instead of url/submit.php. Below is a short example of the JS used for the AJAX request. I'm not sure why it's making incorrect request substitution. It is occurs on both safari and chrome, but not on other computers in the same household.

AJAX request

req=new XMLHttpRequest();
req.open('POST','submit.php');                                                                req.setRequestHeader('Content-type','application/json;  charset=UTF-8');
req.onload=function(resp){
    if (resp.target.status==200){
          do something....
    }
}