fineUploader Failed in the Request To endpoint and the cause in onError Callback is UnKnown Reason - fine-uploader

Question

kindly i have to pages using fineUploader ,
the first page is working correctly but the second isn't : the response in debugging browser console is:
My Html Body will be existing here.
Simple upload request failed for 0
[Fine Uploader 5.11.8] Error when attempting to parse xhr response
text (Unexpected token < in JSON at position 0)
for the point one :(the request didn't reach the endpoint because i made a tester in the endpoint page if any script accessed it)
so the request in the first page is working and the same request with the same path in endpoint property isn't working in the second
i read many articles with the same error but all of them were not identifying correct endpoint path , which i did correctly and tested in the first Page.
var uploader = new qq.FineUploader({
debug: true,
element: document.getElementById('my-uploader'),
request: {
endpoint: "http://localhost/fineuploader/endpoint.php",
// endpoint: "http://localhost/fineuploader/endpoint.php",//commented to prove that i used //both of the relative and absolute paths
},
chunking: {
enabled: true,
concurrent: {
enabled: true
},
success: {
endpoint: "http://localhost/fineuploader/endpoint.php?done",
}
},
deleteFile: {
enabled: true,
endpoint: "http://localhost/fineuploader/endpoint.php"
},
retry: {
enableAuto: true,
showButton: true
},
form:{element:"FormId", },
callbacks: {
onError: function(id, name, errorReason, xhrOrXdr) {
alert(qq.format("Error on file number {} - {}. Reason: {}", id, name, errorReason));
},
});

Answer 1

The Answer of Mr Ray Nicholus Here was useful but i want to provide the solution in my case and my mistake, my problem was that in the first page i didn't provide action attribute in form tag and in the second i did , so when i provided in the second page the action of the form a different value than what is specified in
<form id="test" action="form.php">
request: {
endpoint: "http://localhost/fineuploader/endpoint.php",},
the requests were going to the action attribute value path(form.php) not for the above request value (endpoint.php).

Answer 2

It's really very simple, and there is no other answer to this question: either your endpoint is incorrect (and of course the response will be invalid too) or your endpoint is correct but your endpoint is not returning valid JSON. You'll need to look at the response closely to determine the issue.
In your case, your endpoint is returning HTML, not JSON. You'll have to fix this on your server.