A little background, I'm on the .NET platform using the DataTables plugin on a page and have an API (Web API) that returns the response that the plugin is expecting by default (via the documentation) and in my javascript, I'm attempting to use the ajax api option for DataTables and am getting a 415 response from my API. Now, I can perform a standard fetch to test my API and I get the expected response (200 OK and the response object). Code below:

HTML

<table class="table table-bordered table-hover table-checkable" id="patients">
    <thead>
        <tr>
            <th></th>
            <th>RecordID</th>
            <th>Last Name</th>
            <th>First Name</th>
            <th>Location</th>
        </tr>
    </thead>
</table>

Javascript (doesn't work and I get a 415 Response)

$('#patients').DataTable().clear().destroy();

var args = {
        recordID: $('#recordIdFilter').val().trim() == '' ? null : $('#recordIdFilter').val().trim().replaceAll('-', '').replaceAll('(', '').replaceAll(')', ''),
        firstName: $('#firstNameFilter').val().trim() == '' ? null : $('#firstNameFilter').val().trim().replaceAll('-', '').replaceAll('(', '').replaceAll(')', ''),
        lastName: $('#lastNameFilter').val().trim() == '' ? null : $('#lastNameFilter').val().trim().replaceAll('-', '').replaceAll('(', '').replaceAll(')', ''),
        status: $('#statusSelector').selectpicker('val') == '' ? null : $('#statusSelector').selectpicker('val')
};

var dtable = $('#patients').DataTable({
        responsive: true,
        processing: true,
        ajax: {
            url: '/api/patients/search',
            type: 'POST',
            datatype: 'json',
            data: JSON.stringify(args)
        },
        lengthMenu: [30, 50, 100, -1],
        pageLength: 30,
        order: [[1, 'asc']],
        language: {
            'lengthMenu': 'Display _MENU_',
        },
        headerCallback: function (thead, data, start, end, display) {
            thead.getElementsByTagName('th')[0].innerHTML = `
                                <label class="checkbox checkbox-single">
                                    <input type="checkbox" value="" class="group-checkable"/>
                                    <span></span>
                                </label>`;
        },
        columns: [
            {
                data: 'recordID', width: 'auto', className: 'dt-left', orderable: false,
                render: function (data, type, full, meta) {
                    return `
                                    <label class="checkbox checkbox-single">
                                        <input type="checkbox" value="" class="checkable"/>
                                        <span></span>
                                    </label>`;
                },
            }
            , { data: 'recordID', title: 'ID', width: 'auto', orderable: true }
            , { data: 'lastName', title: 'Last Name', width: 'auto', orderable: true }
            , { data: 'firstName', title: 'First Name', width: 'auto', orderable: true }
            , { data: 'location', title: 'Location', width: 'auto', orderable: true }
        ],
    });

    dtable.on('change', '.group-checkable', function () {
        var set = $(this).closest('table').find('td:first-child .checkable');
        var checked = $(this).is(':checked');

        $(set).each(function () {
            if (checked) {
                $(this).prop('checked', true);
                $(this).closest('tr').addClass('active');
            }
            else {
                $(this).prop('checked', false);
                $(this).closest('tr').removeClass('active');
            }
        });

        showHideNotifyButton();
    });

    dtable.on('change', 'tbody tr .checkbox', function () {
        $(this).parents('tr').toggleClass('active');

        showHideNotifyButton();
    });

Javascript (works and I get a valid response)

fetch('/api/patients/search', {
    method: 'POST',
    body: JSON.stringify(args),
    headers: {
        'Accept': 'application/json',
        'Content-Type': 'application/json'
    }
    }).then(response => response.json())
      .then(data => { console.output(data) });

If Anyone Cares, My API EndPoint

[HttpPost, Route("api/patients/search")]
public async Task<IActionResult> PatientSearch(PatientSearchModel args)
{
    var results = await _patientService.Search(args.RecordId, args.FirstName, args.LastName, args.Status);

    var response = new
    {
        recordsTotal = results.Count,
        recordsFiltered = results.Count,
        data = results.OrderBy(r => r.LastName).ThenBy(r => r.FirstName).ToArray()
    };

    return Ok(response);
}