Problem with datepicker

I tested this feature 2 weeks ago and it worked perfectly. Now it's suddenly broken. Why? https://imgur.com/TlY1r9v I want the date to be displayed like this: YYYY-MM-DD without time. It works 2 weeks ago and now it's broken.. I don't understand why.

code for my datepicker:

    <script type="text/javascript">
            $(document).ready(function(){
                $("#datepicker").datetimepicker({
                    format:'YYYY-DD-MM'
                })
            })
        </script>

choose date:

<div class="card">
        <div class="card-header">
            Choose date

        </div>
        <div class="card-body">
         <input type="text" class="form-control datetimepicker-input" id="datepicker" data-toggle="datetimepicker" data-target="#datepicker" name="date">
        </div>
    </div>

Thank you!