TypeError: $(...).slick is not a function. How to fix?

Question

Slick

I connected the Slick slider, everything works, but for some reason an error is displayed in the panel.
In scripts, jquery is included in the head first, this shouldn't be a problem.

Write: $(document).on('ready', function () {
instead of: $(document).ready(function(){
only destroyed the slider and the horizontal scrolling disappeared.
Maybe the function is written in the old way?
Can someone tell me?
Here Piece of Code:

// Дополнительные Фото
$(document).ready(function(){
$('.gallery').slick({dots:true,infinite:false,speed:300,slidesToShow:4,slidesToScroll:1,responsive:[
{breakpoint:992,settings:{slidesToShow:4,slidesToScroll:4,infinite:false,dots:true,arrows:false}},
{breakpoint:576,settings:{slidesToShow:3,slidesToScroll:3,arrows:false}},
{breakpoint:375,settings:{slidesToShow:2,slidesToScroll:2,arrows:false}}]
});});