Selling out is good news. A back-in-stock flow turns that good news into revenue instead of leaving it on the table. The subscriber who clicked "Notify Me" already went through your product page, decided they wanted the item, and voluntarily gave you their contact details. That is a warmer lead than anyone you will ever reach through a cold campaign. And yet most DTC brands either do not have this flow live at all, or have it set up incorrectly and wonder why it never sends.
This post covers how the flow works, the five mistakes that kill it before it fires, and the sequence structure that converts.
Why Back-in-Stock Is the Highest-Intent Email You Can Send
Automated flows in Klaviyo convert at an average of 1.82% compared to 0.1% for standard campaigns. Back-in-stock flows regularly outperform even that benchmark. The reason is straightforward: the subscriber has already done everything except hand over their money.
They found your product. They read the page. They wanted to buy. The only thing that stopped them was stock. When you notify them the moment stock returns, you are not interrupting their day with a pitch. You are delivering information they explicitly asked for. That changes the entire dynamic.
Compare that to any other email in your sequence. Welcome flows target someone who signed up for a discount. Abandoned cart targets someone who browsed and left. Browse abandonment targets someone who looked but did not add to cart. Back-in-stock targets someone who added to cart, could not check out, and told you they still want it. It is the most qualified list you have.
Back-in-stock subscribers are not prospects. They are deferred buyers. The job of the flow is not to persuade them. It is to remove friction and create urgency before they go elsewhere.
How the Flow Works Technically
The Klaviyo back-in-stock flow requires two components working together. First, a snippet installed on your Shopify product pages that detects when inventory hits zero and replaces the Add to Cart button with a Notify Me button. When a visitor clicks that button, Klaviyo records a Back in Stock Subscribed event on their profile, attached to the specific product variant they wanted.
Second, a triggered flow in Klaviyo that uses the Subscribed for Back in Stock trigger. When Shopify updates inventory and the variant count rises above zero, Klaviyo detects the change, identifies all profiles subscribed to that variant, and begins sending the flow.
The critical dependency is the Klaviyo-Shopify integration. Klaviyo does not check your warehouse. It reads inventory data from Shopify. If that sync has drifted or broken, the trigger will never fire regardless of what your actual stock levels look like.
The 5 Mistakes That Break Your Back-in-Stock Flow Before It Fires
Most of the back-in-stock flows audited either do not send at all or send to the wrong people. Every case traces back to one of these five issues.
Inventory tracking is not enabled in Shopify
Shopify only communicates inventory changes to Klaviyo when Track quantity is enabled on the product. If that setting is off, Shopify never tells Klaviyo the item went out of stock or came back in. Go to each product in Shopify admin, scroll to Inventory, and confirm Track quantity is ticked. Do this for every product you plan to run back-in-stock on.
Continue selling when out of stock is enabled
This Shopify setting is the single most common reason the Notify Me button never appears. When Continue selling when out of stock is on, Shopify treats the product as always available, which means the product page never reaches the out-of-stock state that would trigger the Notify Me button replacement. If you are using this setting for pre-orders or made-to-order products, you will need a custom solution. For standard inventory management, turn it off.
Custom theme compatibility is not handled
Klaviyo's default back-in-stock snippet is built for standard Shopify themes. If your store uses a custom theme, the snippet may not inject correctly and the Notify Me button will either not appear or appear in the wrong position. Klaviyo does not provide support for custom theme implementations. You will need a Shopify developer to integrate the snippet properly.
The first email sends too slowly
Speed is everything on Email 1. The subscriber who signed up for a notification is also watching competitors. If your first email takes 30 minutes to arrive, there is a reasonable chance they have already found an alternative. Set Email 1 to send immediately on trigger, with zero delay. Any delay on the first message is conversion you are giving away for no reason.
Recent purchasers are not filtered out
High-traffic restock events can create a timing gap between when an order is placed and when that order syncs back to Klaviyo. If someone placed an order during a flash restock but the order has not synced yet when the flow fires, they will receive a back-in-stock email for something they just bought. Add a flow filter to exclude profiles who placed an order in the last 24 hours.
The Sequence Structure That Converts
Keep the sequence lean. This is not a nurture flow. These subscribers do not need education. They need the product link and a reason to move now.
Email 1: Immediate send on trigger
Subject line: short, direct, variant-specific. Something like '[Product name] is back in stock' outperforms clever subject lines here. These subscribers are waiting for this email. Make it obvious.
Body: product image, the product name, one sentence confirming it is back, a prominent CTA to the exact product page (not the homepage, not a collection page — the product page), and a short low-stock urgency note if inventory is genuinely limited.
This single email does the majority of the work. Treat it as your highest-value send of the month during a restock.
Email 2: 24 to 48 hours later (conditional)
Only send this if stock is still available. Add a flow filter: Ordered Product in the last 2 days is false. If the subscriber already converted from Email 1, suppress them from Email 2.
Angle: limited stock urgency. 'Only X left' is a simple, honest message when it is accurate. Do not manufacture scarcity. If you have 200 units, do not claim you have 5. If you have 12, say so.
Keep this email short. One image, one line, one CTA.
Email 3: 3 to 5 days later (optional)
This email is for the holdouts. At this point, either they have bought, the product has sold out again, or they have moved on. Suppress anyone who purchased. Check stock before sending.
Two options work here: a secondary product recommendation, or a small incentive if margins allow. Some brands skip Email 3 entirely and see no measurable drop in flow revenue. Test it. If open rates on Email 3 are below 15% and conversion is negligible, remove it.
Add SMS for Time-Sensitive Restocks
For high-demand products where stock is genuinely limited, run email and SMS in parallel on Email 1. SMS reaches subscribers within seconds and is particularly effective when you are restocking a small quantity of a hero SKU that will sell out again quickly.
The setup in Klaviyo is straightforward: add an SMS message alongside the email at the same step in the flow, configured to send only to profiles who have an active SMS consent status. Profiles who only opted into email get the email sequence. Profiles who opted into both get both.
Keep SMS copy minimal. Product name, availability confirmation, and a short link. Treat them as complementary channels covering the same urgent moment from different angles, not as duplicates of each other.
What Good Benchmarks Look Like
Open rates above 60% on Email 1 are normal for a properly configured back-in-stock flow. Click-through rates of 15 to 25% are achievable. Conversion rates of 5 to 12% are realistic for a first email to a warm, intent-confirmed subscriber list.
If your numbers are significantly below those figures, the issue is almost always one of the five setup mistakes above, or a delay on Email 1 that is letting the moment cool. Fix the mechanics first. Copy improvements are secondary.
Klaviyo's own benchmark data shows automated flows average 1.82% conversion across all flow types. Back-in-stock, when set up correctly, sits well above that average. If yours is at or below 1.82%, something in the setup is wrong.
About the Author
Caner Veli built Liquiproof from zero to 3,000+ global retailers in under 6 years. He now helps DTC and CPG brands fix broken growth engines and scale 2x to 15x in 90 days.
Work With Purposeful Profits
Your back-in-stock flow should be running this week.
If you are selling out and not recapturing those buyers with a properly configured Klaviyo flow, you are leaving your highest-intent revenue on the table. Get in touch and we will identify exactly what is broken in your current setup.
Fix Your Email FlowsFrequently Asked Questions
How does the Klaviyo back-in-stock flow work?
Klaviyo's back-in-stock flow triggers automatically when a product's inventory is restored in Shopify. It requires a snippet on your product pages that swaps the Add to Cart button for a Notify Me button when stock hits zero, and a triggered flow in Klaviyo that fires the moment inventory is restored. Subscribers receive an email (and optionally an SMS) with a direct link to the product.
Why won't my Klaviyo back-in-stock flow send emails?
Check four things in this order: inventory tracking is enabled in Shopify under Track quantity; Continue selling when out of stock is turned off; your theme is compatible with Klaviyo's snippet; the Klaviyo-Shopify integration is syncing correctly. The majority of non-sending flows trace back to one of these four issues.
How many emails should a back-in-stock flow have?
One to three emails. Email 1 goes out immediately on trigger and does most of the revenue work. Email 2 at 24 to 48 hours adds urgency if stock is still limited. Email 3 at 3 to 5 days is optional and works best as a related product recommendation or a small incentive. Always suppress converted subscribers from Emails 2 and 3.
What conversion rate should I expect from a back-in-stock flow?
Email 1 on a properly configured flow typically converts at 5 to 12%, with open rates above 60%. Klaviyo's overall benchmark for automated flows is 1.82%. If your back-in-stock flow is converting below that, the issue is almost always a setup problem, not a copy problem.
Should I use SMS for back-in-stock alerts?
Yes, for high-demand, limited-stock restocks. Send email and SMS simultaneously on Email 1 for subscribers who have both consents. Keep SMS copy minimal: product name, one-line confirmation, and a short link. Treat it as a parallel channel rather than a replacement for email.