Quick Answer: A Klaviyo abandoned cart flow can only message a shopper Klaviyo actually saw and identified. Most flows miss buyers not because the emails are bad, but because the triggering event never fired, the shopper was never identified, or both, especially for express checkout users on Shop Pay or Apple Pay. Fixing event capture and identity at the data layer, not the email copy, is usually where the real revenue is.

Key Takeaways

• If a shopper isn't identified and the triggering event never reaches Klaviyo, no amount of email copywriting can recover them, the flow simply never fires.
• Express checkout (Shop Pay, Apple Pay, PayPal) is the most commonly missed abandonment path, since it skips the pages standard tracking depends on, and these are often your highest-intent buyers.
• Rezy Design fixed event capture and identity at the data layer with no new flows or copy, and saw a 106.17% lift in abandoned cart flow revenue and a 51.2% lift in total Klaviyo-attributed revenue.
• Low flow entry counts point to a tracking and identity problem. Healthy entry counts with weak opens and clicks point to a deliverability or content problem. Fixing the wrong one wastes effort.
• Two separate flows, one for cart abandonment and one for checkout abandonment, outperform a single flow trying to serve both audiences at once, since the two groups need different timing and tone.

What does it actually mean when a Klaviyo flow "misses" buyers?

It means the triggering event never reached Klaviyo, or Klaviyo received the event but couldn't tie it to a known profile. Either way, the email that was supposed to fire never had a chance to.

In practice, this shows up a few specific ways: a shopper abandons and no event fires at all, so nothing triggers. A shopper browses anonymously, so Klaviyo has no profile to message even if the event arrives. A shopper starts checkout through Shop Pay or Apple Pay, but the flow only listens for Added to Cart, so the highest-intent abandoners slip through entirely. Or a shopper buys later on a different device, and attribution gets messy enough that you can't tell whether the flow even worked.

The common thread across all four isn't messaging quality. It's events and identity.

Why can't Klaviyo message someone it can't identify?

Because Klaviyo can only send an abandoned cart email if it can tie cart activity to a known profile, and identity gets lost constantly on a purely client-side setup. A shopper who browses on mobile and returns on desktop looks like two strangers to a system that only tracks browser sessions.

This is the same underlying problem that quietly drags down Meta Pixel match quality and Meta ROAS. On Shopify, the same gap shrinks your recoverable Klaviyo audience instead. The fix is cross-device identity stitching, recognizing a returning shopper across sessions and devices and connecting their anonymous browsing history to the profile they eventually reveal. We've covered the full mechanism behind this separately, but the short version: when Rezy Design turned this on, the same identity improvements that lifted their Meta event match quality from 5 to 7 also expanded the pool of shoppers Klaviyo could actually reach.

Here is Rezy Design’s success story by using Aimerce.

Why is client-side tracking quietly dropping events before they reach Klaviyo?

Because most Added to Cart and Checkout Started events depend on a browser script executing successfully, and ad blockers, Safari's tracking prevention, and slow-loading scripts all interfere with that. You end up seeing fewer add-to-carts in Klaviyo than Shopify actually recorded, checkouts Klaviyo never witnessed, and payloads missing product details.

This is exactly why ad platforms moved to server-side delivery through the Conversions API: it doesn't depend on the shopper's browser successfully executing every script. Your email platform deserves the same reliability. Server-side tracking captures events at the source and delivers complete, enriched payloads to Klaviyo the same way a Conversions API integration does for Meta.

Why is express checkout creating a blind spot in your flows?

Because Shop Pay, Apple Pay, and PayPal let shoppers skip the cart and standard checkout pages entirely, and if your tracking was built around the traditional cart-to-checkout path, these shoppers generate the fewest signals despite being your fastest, highest-intent buyers.

A shopper who taps Shop Pay, sees the shipping cost, and closes the sheet is arguably the single most valuable abandoner in your store. Most Klaviyo setups never see them at all.

What other setup mistakes quietly shrink flow entry, beyond missing events?

Two common ones: triggering on a single event by default rather than by design, and filters that require an optional property most incomplete client-side data never actually populates.

Many flows trigger on Added to Cart alone simply because it's the default, not because it's the right choice. That setup misses shoppers who jump straight to checkout without a traditional add-to-cart step. The opposite setup, triggering only on Checkout Started, misses shoppers who build a cart and stall before checkout. Treat recovery as a two-stage problem, cart-building intent and checkout intent, and cover both with separate flows.

Separately, a filter that requires an optional property, like item_names or cart_value, quietly excludes every profile where that property never arrived. With incomplete client-side data, that can be a meaningful share of your audience. Start broad, keep filters minimal, and add sophistication only after you've confirmed event completeness.

Client-Side vs. Server-Side Event Capture for Klaviyo Flows

How do you actually recover the missing buyers, step by step?

Fix the data first, then the messaging, in that order, since better copy can't trigger a flow that never fires.

1. Audit event coverage before touching copy. In Klaviyo, review recent volume for Viewed Product, Added to Cart, Started Checkout, and Placed Order, and compare it directionally against Shopify's own analytics. If add-to-carts or checkouts look too low in Klaviyo relative to Shopify, your flows are under-triggering, and no amount of copywriting fixes that.

2. Move event capture server-side. A server-side tracking setup captures events at the source, stitches identity across devices and sessions, and delivers enriched events to Klaviyo, Meta, and Google at the same time. The result is more abandoners entering your flows with complete cart context: products, values, and a working checkout link. This was the entire intervention at Rezy Design, no new flows, no new creative, just better signal in.

3. Capture email earlier, without being annoying. Even perfect tracking can't message a shopper who never identifies. A cart drawer email capture ("email me my cart"), a lightweight welcome offer, and encouraging Shop Pay or account login all make identity more durable, with one clear benefit and minimal fields.

4. Run two complementary flows, not one. Flow A, Abandoned Cart, triggered by Added to Cart. Flow B, Abandoned Checkout, triggered by Checkout Started including express checkout starts. Each should check for purchase before sending, personalize with the best available cart data, and match timing to intent, checkout abandoners need a first touch within 30 to 60 minutes, cart abandoners can wait 2 to 4 hours.

5. Make flow logic resilient to missing properties. If item details exist, use a dynamic product block. If not, send a generic reminder with a link back to cart. You still recover the shopper even when enrichment is incomplete.

6. Handle the actual objection, not just the reminder. Late-stage abandonment is usually an objection problem, not a forgetting problem. Cover shipping timelines, payment options, price framing with reviews and guarantees, and a plain-text fallback that invites a reply if something broke at checkout.

Common mistakes to avoid

• Blaming deliverability before checking tracking. If flow entry counts are low relative to your store's actual cart and checkout activity, the problem is tracking and identity, not inbox placement. Fixing deliverability won't reach a shopper who never entered the flow.
• Running one flow for both cart and checkout abandonment. The two audiences need different timing and tone. A single flow trying to serve both mistimes at least one of them.
• Requiring optional properties in filters. This silently excludes any profile where that property never arrived, often a large share of your audience with incomplete client-side data.
• Assuming more events captured is automatically better. A small set of high-value events (Add to Cart, Begin Checkout, Purchase) captured consistently and tied to profiles outperforms a larger set captured unreliably.
• Rewriting email copy before auditing event coverage. If the flow isn't being entered in the first place, better copy inside it changes nothing.

FAQ

Why does Shopify show more carts and checkouts than Klaviyo? Shopify observes activity directly in its own storefront and checkout environment. Klaviyo depends on events being sent from your site, usually by browser scripts. When those scripts are blocked by ad blockers or privacy features, or when the shopper is anonymous, Klaviyo sees fewer events. Server-side tracking closes most of this gap by capturing events at the source instead of in the browser.

Does server-side tracking improve Klaviyo abandoned cart flows? Yes, in two ways. It increases the number of abandonment events Klaviyo receives, since delivery no longer depends on the shopper's browser, and it enriches each event with complete cart and product data so dynamic blocks and filters work reliably. Rezy Design saw a lift in abandoned cart flow revenue after moving to server-side capture with identity stitching.

Can Klaviyo see shoppers who abandon Shop Pay or Apple Pay checkouts? Usually not with a standard client-side setup, since express checkout skips the pages where traditional tracking fires. These are often your highest-intent abandoners. Capturing express checkout events server-side lets these shoppers enter your abandoned checkout flow like any other.

Should I trigger my flow on Added to Cart or Checkout Started? Both, in separate flows. Checkout abandoners are closest to purchase and need a fast, direct first touch. Cart abandoners need more context and reassurance. One flow trying to do both will mistime one of the two audiences.

How do I know whether my flow is failing because of tracking or deliverability? Compare flow entry counts to your store's actual cart and checkout activity. Low entry counts point to tracking and identity. Healthy entry counts with poor opens and clicks point to deliverability and content. Fix tracking first, since no deliverability work can reach a shopper who never entered the flow.

Does fixing tracking data mean I need to rewrite my flow emails? Not necessarily. Rezy Design's result came entirely from fixing event capture and identity, using the same flows and copy they already had. Better signal in generally means better results out, without touching the messaging at all.

What's the fastest way to check if my flow has a tracking problem? Compare Klaviyo's recent event volume for Added to Cart and Started Checkout against Shopify's own analytics for the same window. A meaningful gap between the two is the clearest sign your flows are under-triggering rather than under-performing.

Sources

[1] Aimerce Success Stories, "Rezy Design case study"

Related reading

• Cross-Device Stitching: Connecting Mobile Safari Discovery to Desktop Chrome Purchases
• Top 5 Abandoned Cart Apps for Shopify in 2026
• What Is EMQ Score and Why It's Silently Killing Your Meta ROAS