I am getting net::ERR_TOO_MANY_REDIRECTS in PHP code

I am getting net::ERR_TOO_MANY_REDIRECTS

When I search treatments according to the department dropdown getting error and jquery is not working,jquery is not loading and the dependent dropdown is not working

<script>
       $(document).ready(function() {
        // When the department dropdown is changed
        alert('Hi');
        $('#department').on('change', function() {
            var departmentId = $(this).val();
            var departmentName = $(this).find('option:selected').text();

            if (departmentId) {
                $.ajax({
                    url: 'get_treatments.php',
                    type: 'POST',
                    data: {
                        department_id: departmentId,
                        department_name: departmentName
                    },
                    success: function(response) {
                        $('#treatment').html(response);
                        updateDepartmentName(departmentId, departmentName);
                    }
                });
            } else {
                $('#treatment').html('<option value="">Select Department first</option>');
            }
        });

alert not working