Using Facebook Pixel To Track Klaviyo Submissions in Shopify

Hi there, I've read everywhere and I'm really unsure how to set this up.

I have already installed my Pixel through the Facebook and Instagram Sales Channel App on Shopify. I have ran campaigns before on Facebook  and all has worked well.

I am trying to run a campaign to optimise for Klaviyo sign ups and therefore would like to use my pixel to track the sign ups submissions on site.

To do this I have added my pixel code to theme.liquid in the header section:

 <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', '335819078856330');
      fbq('track', 'PageView');
    </script>
    <noscript
      ><img
        height="1"
        width="1"
        style="display:none"
        src="https://www.facebook.com/tr?id=335819078856330&ev=PageView&noscript=1"
    ></noscript>

Which I'm not sure why I should have to be honest if the pixel has already been set up through the app. 

I also added the Klaviyo call code at the bottom of my theme.liquid file

 </script>
    {% endif %}
    <script>
      window.addEventListener("klaviyoForms", function(e) {
          if (e.detail.type == 'submit') {
              fbq('track', 'Lead');
          }
      });
    </script>

This I am sure would track every submit event and call it Lead to the Pixel.
Now running test data - it hasn't captured a single lead. In my Meta dashboard, the standard event of Lead isn't even appearing.

I am so confused, and unsure what to do.

Please help!

Thanks in advance.