Наверняка поэтому ;)
(index):73 Uncaught TypeError: $(...).datepicker is not a function
at HTMLDocument. ((index):73)
at c (jquery.min.js:4)
at Object.fireWith [as resolveWith] (jquery.min.js:4)
at Function.ready (jquery.min.js:4)
at HTMLDocument.q (jquery.min.js:4)
В каком месте ты подключаешь скрипт?
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
<link rel="stylesheet" href="https://code.jquery.com/ui/1.12.1/themes/base/jquery-ui.css">
<script src="https://code.jquery.com/ui/1.12.1/jquery-ui.js"></script>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/datepicker/1.0.9/datepicker.css">