AJAX call not working properly

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C#

Ajax

jQuery

.NET-Core

I am working with a .net core web project. I have to send a value from javascript to razor pageModel. But the problem is I can't get value from pageModel in JSON format. It returns the source code of whole cshtml page. I have tried each and every solution I found. Here is what I have tried recently

What I have tried:

AJAX

$.ajax({
    type: "POST",
    url: '/index?handler=RetData',
    headers: {
        Accept: "application/json; charset=utf-8"
    },
    beforeSend: function (xhr) {
        xhr.overrideMimeType("application/json; charset=utf-8")
    },
    data: AddAntiForgeryToken({ 'oldEmail': oldEmail }),
    dataType: "json",
    success: function (retValue) {
        alert(retValue);
    },
    error: function (e) {
        var msg = "Error!" + e.message;
        alert(msg);
    }
});

index.cshtm.cs Code:

[HttpPost]
[ValidateAntiForgeryToken]
public JsonResult OnPostRetData([FromBody] JObject jobject)
{
    try
    {
        JObject job = new JObject();
        job.Add("Album", "Me Against The World");
        return new JsonResult(job);
    }
    catch (Exception ex)
    {
        throw ex;
    }
}