HTTP Error 431 on local machine in a C# MVC application

Question

I'm getting an HTTP Error 431 in a C# MVC application in a View after ajax sends data to my controller. This is the code in my View:

 $.ajax({
        type: "POST",
        url: "@Url.Action("SaveElectionData")",
        dataType: "text",
        data: { 'formData': sendData },
        success: function (msg) {
            alert("back in view, success");
            $("form").submit();
        },
        error: function (req, status, error) {
            alert("back in view, fail");
            $("form").submit();
        }
 });

When I run the application, the ajax sends data to my controller. The controller processes the data and returns a string to the ajax. I get the alert back in view, success . As soon as I click the button to close the alert, I get the 431 error.

When I look at dev tools and look at network, this is what I see:

And when I click on Updated this is what I see:

I am running this on a development machine (a mac) running Visual Studio 2022 and I assume IIS Express (provided by Visual Studio unless its different on a mac as opposed to a windows machine) and I had just cleared out the browser (chrome) cookies. Also, according to the second image, the content length of the request header is only 182.

And this is the code in the view for the form:

@using (Html.BeginForm("Updated", "OnlineEnrollment", FormMethod.Post))
{
}

I do not have any elements in the form since the ajax has already sent the data to the controller.

So why would I be getting this 431 error?

Any ideas?