Hi digital marketers, this is Faisal Amin. In this 2025 updated tutorial I show you the full step-by-step process to set up Klaviyo server-side tracking using Server-Side Google Tag Manager. First, I make sure the basics are correct: your website is connected with GTM, your dataLayer events are firing, and you can see the eCommerce event parameters in Tag Assistant (page_view, view_item, add_to_cart, begin_checkout, purchase). Then I use the Stape.io Data Tag template in the web container to send all event data and parameters from browser to server, and I set a constant variable for my server-side URL so I don’t do copy-paste again and again. After that, I move to the server container and receive the data using the Data Client template (imported from the template file). Then I configure the Klaviyo server-side tag (Stape.io template), create a Klaviyo Private API Key, and store it as a constant variable. I show how I build the items array using an Object Builder (put object inside array) so Klaviyo gets product-level details like product id, sku/id, product name, and quantity. Finally, I set up begin_checkout and purchase, and for purchase I send customer properties like email, phone, first name, last name, street, city, region, postal code, and country. By the end, you can verify in server preview (“post to update / accepted”) and then check in Klaviyo profiles where the events appear.