jQuery issue Uncaught TypeError: jQuery(…).countdown is not a function

Hello, im getting this jQuery error in my console log in a localhost –

Uncaught TypeError: jQuery(…:wink:.countdown is not a function at theme.js:3

The actual code is

jQuery('#clock').countdown('2020/10/10', function(event) {
var $this = jQuery(this).html(event.strftime(''
+ '<span>%w</span> weeks '
+ '<span>%d</span> days '
+ '<span>%H</span> hr '
+ '<span>%M</span> min '
+ '<span>%S</span> sec'));
});

Whats wrong with my code?