TypeError: option timepicker is not recognized! it is shown

Question

<script type="module">
    document.addEventListener('DOMContentLoaded',function(){
        var calendarEl = document.getElementById('calendar');
        var calendar = new FullCalendar.Calendar(calendarEl , {
            initialView: 'dayGridMonth',
            initialDate: new Date(),
            headerToolbar: {
                left: 'prev,next,today',
                center: 'title',
                right: 'dayGridMonth,timeGridWeek,timeGridDay',
            },
            dateClick: function(info){
                console.log(info);
                initializeStartDateEndDateFormat('Y-m-d',true);
                $('#exampleModal').modal('show');
            },
        });
        calendar.render();
    });
    function initializeStartDateEndDateFormat(format, allDay){
        let timePicker = !allDay;
        $('#startDateTime').datetimepicker({
            format : format,
            timepicker:timePicker
        });
        $('#endDateTime').datetimepicker({
            format : format,
            timepicker:timePicker
        });
    }
</script>

this is the code i wrote and cdn is perfect but still this error arises can't understand what the issue is.