datepicker is not a function TypeError

hi,

I want disable Mobile Keyboard in the datepicker form (jquery). You can find it here: https://nueva.bycamper.es/reserva-tarifas/ I did it with a snipped:

<script type="text/javascript">
    jQuery(function() {
         jQuery( ".datepicker" ).datepicker({ }).attr('readonly','readonly');
    });
</script>

And it works well... until I looked in the console and it says: jQuery.Deferred exception: jQuery(...).datepicker is not a function TypeError: jQuery(...).datepicker is not a function.

mmm, do you know how I can avoid that error?

Thank you very much.