slick이 작동되지 않는 문제

안녕하세요,

슬릭 슬라이더가 작동되지않고

jQuery.Deferred exception: $(...).slick is not a function TypeError: $(...).slick is not a function

이런 메세지가 나오는데요...

첨부해주신 단계별 코드를 보면서 하나하나 다 비교도 해보고 slick js, css 파일도 옮겨서 덮어써보고, jquery도 최신으로 바꿔봐도 슬릭 슬라이더만 작동이 되지 않는데 왜 그런 걸까요?

index.html

<head>
 <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>DesignWorks Architecture Agency</title>
  <script src="https://code.jquery.com/jquery-3.5.1.min.js"></script>
  <!-- Page Scroll Effects JS & CSS -->
  <script src="js/velocity/modernizr.js"></script>
  <script src="js/velocity/velocity.min.js"></script>
  <script src="js/velocity/velocity.ui.min.js"></script>
  <script src="js/velocity/main.js"></script>
  <link rel="stylesheet" href="js/velocity/velocity.css">
  <!-- Smooth Scrolling -->
  <script src="js/jquery.scrollTo.min.js"></script>
  <!-- Slick.js -->
  <link rel="stylesheet" href="js/slick/slick.css">
  <link rel="stylesheet" href="js/slick/slick-theme.css">
  <script src="js/slick/slick.min.js"></script>
  <!-- Custom JS & CSS -->
  <script src="custom.js"></script>
  <link rel="stylesheet" href="style.css">
  <link rel="stylesheet" href="responsive.css">
	<script src="https://kit.fontawesome.com/62a31d096f.js" crossorigin="anonymous"></script>
</head>

custom.js

$(function(){
  // Trigger
  $('.trigger').click(function(){
    $(this).toggleClass('active')
    $('.gnb').toggleClass('active')
  })
  $('section, .menu a').click(function(){
    $('.gnb').removeClass('active')
    $('.trigger').removeClass('active')
  })
  
  /* Smooth Scrolling */
  $('.menu a, .gototop').click(function(e){
    $.scrollTo(this.hash || 0, 900)
  })
  
  // Change CSS with Scroll
  $(window).scroll(function(){
    if($(window).scrollTop() > 50) {
      $('header, .gototop').addClass('active')
    }
    else {
      $('header, .gototop').removeClass('active')
    }   
  })
  
  // slick.js : history
  $('.history-slider').slick({
    dots: true,
    infinite: false,
    speed: 300,
    slidesToShow: 4,
    slidesToScroll: 2,
  })
	
	// slick.js : project photo
	$('.project-photo').slick({
		dots: true,
		infinite: true,
		speed: 500,
		fade: true,
		autoplay: true,
		autoplaySpeed: 2000,
		cssEase: 'linear'
	})
})

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