If you are using Shopify as an e-commerce platform, then you will have to go to Settings -> Checkout -> Order processing -> Additional content and scripts and add the code below in the text area (see image below).

Replace the following placeholders with the program and order values:
CAMPAIGN_UNIQUE: you received it by e-mail
CONFIRM: you received it by e-mail

<iframe height='1' width='1' scrolling='no' marginheight='0' marginwidth='0' frameborder='0' src='{{ subtotal_price | money_without_currency }}&campaign_unique=CAMPAIGN_UNIQUE&confirm=CONFIRM&description={{ cart.items }}&transaction_id={{ order.order_number }}'><iframe>
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