Replace <insert_pixel_id> with the Facebook pixel id

shopify-fb-tracking.liquid

{% if first_time_accessed %}
  <!-- Facebook Pixel Code -->
  <script>
  !function(f,b,e,v,n,t,s)
  {if(f.fbq)return;n=f.fbq=function(){n.callMethod?
  n.callMethod.apply(n,arguments):n.queue.push(arguments)};
  if(!f._fbq)f._fbq=n;n.push=n;n.loaded=!0;n.version='2.0';
  n.queue=[];t=b.createElement(e);t.async=!0;
  t.src=v;s=b.getElementsByTagName(e)[0];
  s.parentNode.insertBefore(t,s)}(window, document,'script',
  'https://connect.facebook.net/en_US/fbevents.js');
  fbq('init', '<insert_pixel_id>');
  fbq('track', 'PageView');
  </script>
  <noscript><img height="1" width="1" style="display:none"
  src="https://www.facebook.com/tr?id=<insert_pixel_id>&ev=PageView&noscript=1"
  /></noscript>
  <!-- End Facebook Pixel Code -->
  <!-- Facebook Pixel Event - Purchase -->
  <script>
    window.addEventListener('DOMContentLoaded', () => {
      console.log('Initiated Event - Purchase')
      fbq('track', 'Purchase', {
        content_type: 'product',
        content_name: [{%- for line_item in order.line_items -%}'{{ line_item.title }}'{%- unless forloop.last -%},{%- endunless -%}{%- endfor -%}],
        content_ids: [{%- for line_item in order.line_items -%}'{{ line_item.sku }}'{%- unless forloop.last -%},{%- endunless -%}{%- endfor -%}],
        currency: '{{ shop.currency }}',
        num_items: {{ checkout.line_items | size }},
        value: parseFloat('{{ checkout.total_price | money_without_currency }}')
      });
    });
  </script>
{% endif %}