What server-side does for Klaviyo
Onsite + Server-side in parallel
klaviyo.js catches on-site browsing, server-side fills in the e-commerce events (Placed Order, Started Checkout) the browser blocked. Klaviyo deduplicates, so an event is never counted twice.
Profile identity (email / phone)
We send every server-side event with a profile identifier (email or phone), so Klaviyo attaches it to the right contact — even when the browser never runs klaviyo.js.
Accurate flows and segments
Abandoned-cart, post-purchase, and win-back flows fire on the server-side truth, not leaky browser data. Segments based on real purchase behavior.
No per-event fee
Klaviyo is one of 18 supported platforms in the plan from CZK 349. No fees per event.
Three steps and the data flows.
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1
Sign up + set up the container
14 days free, the setup wizard generates the GTM container. Import it and you're done.
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2
Add your Klaviyo Public + Private API key
In Klaviyo → Settings → API Keys you get the Public (company ID) and Private key. Enter them in the DataNostro dashboard and pick your e-commerce events.
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3
Verify in the Klaviyo Activity Feed
Klaviyo → Analytics → Activity feed shows incoming server-side events tied to profiles. Test with a sandbox profile.
What's in every plan
No surcharges per event, no cap on contacts.
klaviyo.js + Events API in parallel.
Event tied to email / phone.
Correct Klaviyo date format.
Placed Order, Checkout, Viewed Product…
QA conversions before going live.
Custom events and properties.
No per-pixel charges. Unlimited platforms.
Klaviyo + 17 more platforms (Sklik, Heureka, GA4, Google Ads, TikTok…) in one STARTER plan from CZK 349/month. No per-pixel surcharges.
Frequently asked questions
Does this replace klaviyo.js? +
No — we recommend both. The onsite script catches browsing, server-side fills in the e-commerce events the browser loses. Klaviyo deduplicates.
How do you match events to a profile? +
We send an identifier (email or phone) with every event. Klaviyo uses it to find or create the profile and attaches the event to it.
Do you handle the Klaviyo date format? +
Yes — we send timestamps in ISO-8601 exactly as Klaviyo expects. This is the most common pitfall when setting up the Events API by hand.
Do flows and segments work with it? +
Yes — server-side events trigger flows (abandoned cart, post-purchase) and feed segments exactly like onsite tracking, just on more complete data.
Flows are only as smart as the data that triggers them
Abandoned-cart and post-purchase flows misfire on lost events. Server-side via DataNostro feeds Klaviyo complete data. Five-minute setup, 14-day free trial.