Add the pixel to Shopify
Add the tracking code to your Shopify by editing your theme's source code.
Step-by-step guide:
From your Shopify admin, go to Online Store > Themes
In the Current theme section, click Actions, and select Edit code
Click the theme.liquid file to open the code editor
Add your Proofly pixel code. This must be between the <head> and </head> tags
Click Save
Notice: Be careful on editing code, you may break your store's layout.