Klaviyo Back In Stock Flow: Turning Sellouts Into A Waitlist That Buys

A Klaviyo back in stock flow sends an alert to shoppers who asked to hear when a sold-out product returns. Each person on that list clicked a “Notify me” button on a product page for one specific size or color, so the list is demand you’d otherwise lose the moment a variant sells out. A big sale like Black Friday can sell out popular variants, and each sold-out variant can start a list.

For a Shopify store already running Klaviyo, the flow itself is short: a trigger, a back in stock delay and usually one message. Whether it sells anything depends on the form, on the stock counts Klaviyo reads from Shopify, and on how many people you let hear about each restock. Set that last part wrong and a restock of 40 units can alert 500 people at once, which leaves at least 460 of them clicking through to a product that’s sold out again.

When a shopper signs up, Klaviyo records a “Subscribed to Back in Stock” (opens in new tab) event against the variant they picked, and that event starts the flow. A custom metric can’t stand in for it. Right after the trigger sits a back in stock delay, a special step where subscribers wait until their item is restocked, followed in most flows by a single email or text. You don’t need extra time delays, because the back in stock delay handles the timing.

That makes the Klaviyo back in stock flow different from an abandoned cart flow. A cart flow reads intent from what a shopper did and has to decide when to nudge them. A back in stock subscriber told you which variant they want, and the flow waits until you can sell it to them.

Among the lifecycle flows a Shopify store runs on Klaviyo, back in stock is the one that depends on your inventory data as much as on shopper behavior. If Shopify’s stock counts are wrong, the alert goes out at the wrong time or not at all.

Turn off Smart Sending on the Klaviyo back in stock alert so it reaches everyone who asked for it, and leave Smart Sending on for messages that aren’t essential. Klaviyo also advises against trigger filters and profile filters on this flow.

Subscribers sit in a Waiting list at the back in stock delay, and View details in the flow’s Performance section shows who’s there. When a variant is restocked, your back in stock settings decide how many people move on to the message, and the oldest subscribers go first. Notifications can go out in batches, so some people stay in Waiting for a later batch.

One status setting can keep the queue empty. The message after the delay has to be Live or Manual (opens in new tab), and if it’s in Draft, no one is added to the waiting list. Manual holds each message for you to review before it sends, while Live sends on its own.

So turn the flow on before a product sells out, not after. Adding past profiles to a Klaviyo back in stock flow usually won’t bring new people in. To reach the people listed in your back in stock report, send a campaign instead, built on Klaviyo segments if you want to leave out recent buyers, since the flow itself shouldn’t carry those filters.

A Klaviyo back in stock subscription clears once the alert for that variant goes out (opens in new tab), and the shopper can sign up again. Each shopper holds one subscription per variant at a time and can subscribe to as many different variants as they like.

If your storefront is custom or headless, signups go through the Create Back In Stock Subscription (opens in new tab) endpoint in Klaviyo’s API, which ties each subscription to a catalog variant and accepts email, push, SMS and WhatsApp. The Klaviyo back in stock flow itself also works on other platforms and on inventory-aware custom catalogs, but the form editor described below is for Shopify and BigCommerce stores.

Klaviyo back in stock forms are built in Klaviyo’s form editor, and they’re available to stores with an enabled Shopify or BigCommerce integration (opens in new tab). Once you publish the form, a Notify me button appears on out-of-stock product pages that match your targeting, and it shows and hides with inventory. You choose whether the button replaces the add to cart button or stacks with it.

Only one back in stock form can exist per account, published or draft, so delete an old one before you build another. On Shopify, you can include or exclude products by product tag under Targeting. Use that to keep the button off products you won’t restock.

Shopify’s “Continue selling when out of stock” (opens in new tab) setting lets customers buy a product or variant at zero or below, and you can only turn it on when inventory tracking is on. If it’s on for a product, the Klaviyo back in stock button won’t appear (opens in new tab) and no restock alerts send for it.

Shopify lists preorders among that setting’s uses, and that’s a choice to make product by product. A waitlist captures demand without taking money. Selling pre-orders on Shopify takes payment up front, and a variant set to keep selling at zero won’t show the Notify me button, so pick one route for each product.

Inventory tracking has to be on for every variant you take signups on, and the counts have to match what’s actually on the shelf. Good inventory management is what tells Klaviyo a restock happened, so fix stock counts before you build the flow.

The form needs Klaviyo’s onsite tracking, Klaviyo.js, installed before you publish it. On Shopify, you turn that on by enabling the Klaviyo app embed (opens in new tab) in the theme editor’s App embeds tab and checking “Track behavioral events” under Integrations > Shopify in Klaviyo. A new theme needs the embed enabled again, so if you switch themes before a big sale, check it the same day.

Some stores still have Klaviyo’s older code-based back in stock install in their theme. Remove it before you publish the new form by searching theme.liquid for backinstock and deleting the snippet, or shoppers can see two buttons. That code-based install is only supported on certain free Shopify themes (opens in new tab) such as Dawn and Sense, and new setups go through the form editor.

Two theme details can hide the button. If your theme hides a product once every variant is sold out, edit product.liquid so it still displays, because the button lives on that page. If you’re on the Retina theme, turn off its built-in Notify Me button so it doesn’t compete with Klaviyo’s.

If you sell in retail stores on Shopify POS, the Klaviyo back in stock flow counts inventory in your physical stores and your warehouse together (opens in new tab). Shopify decides whether a product shows as out of stock online from the location that fulfills online orders (opens in new tab), even when another location has units. Put those together and units arriving at a store could count toward a restock alert for a variant your online store still shows as sold out. Test it on one variant before you rely on it.

Three settings control what happens when stock comes back, and they apply account-wide to every back in stock flow. You edit them in Settings > Other > Back in stock settings, or from the flow builder. The tab only appears after at least one shopper has subscribed, so submit a test signup on a sold-out variant before you go looking for it.

The restock minimum (opens in new tab) is how many units have to be in stock before any Klaviyo back in stock alert goes out. The notification quantity is either everyone at once, which is the default, or a batch size counted per unit restocked. The notification frequency is how long Klaviyo waits between batches, in hours or days.

Each batch goes to the oldest subscribers first. With 20 units restocked at 5 subscribers per unit, the oldest 100 subscribers get the first alert. Batches keep going until inventory falls below your restock minimum, and then the Klaviyo back in stock flow stops sending.

Here’s how that plays out on a hypothetical variant with 500 people waiting and 40 units arriving. On the default, all 500 get the alert at once, and at least 460 of them can’t buy. At 5 per unit, the oldest 200 hear first, and at 2 per unit, the oldest 80 do. Everyone else waits for a later batch, which goes out only if stock hasn’t dropped below your minimum when its turn comes.

If people tell you they signed up for a Klaviyo back in stock alert and heard nothing, check the minimum and the batch size first. A Klaviyo community manager suggested two likely causes (opens in new tab) for missing alerts: the flow stops sending once inventory drops below the minimum, and with batching, later groups may not be reached before a popular item drops below it.

Set the batch size from the queue you actually have. Before the stock lands, export the Currently Queued Subscribers CSV (opens in new tab) from the back in stock delay’s reports, with the date range set to All Time. It lists each waiting subscriber with the SKU, variant ID, product title and variant title, so you can count how many people are waiting on each variant you’re about to receive. Only account owners and admins can export it.

Restocks can arrive a few units at a time for one variant. Set the restock minimum high enough that a one- or two-unit trickle doesn’t alert anyone, and set the wait between batches long enough for the first group to buy before the next group hears. Your own past restocks are the best guide to how many alerted shoppers buy, so check them before you pick a batch size.

Keep the back in stock email to one message. Klaviyo can’t check inventory before a second message (opens in new tab) in the flow, so a reminder can go out for a product that’s already sold out again.

Start from the pre-built template by searching “back in stock” under the Email templates tab. The back in stock email pulls product details from your catalog at send time (opens in new tab), using the variant ID from the signup, so a price or title that changed while the shopper waited is current in the alert. You can show the product title, price, variant title and the variant image, which falls back to the product image when a variant has none.

Point the button at the variant URL, the product URL plus ?variant= and the ID, so the shopper lands on the size or color they asked for. Keep the template’s table block static, not dynamic. The shopper already knows what they want, so the email needs the product, the variant, the price and one button, and little else.

SMS has to be turned on (opens in new tab) in your Klaviyo account first, and the text only goes to people who are already SMS subscribers. On the form, a phone field can sign shoppers up for an alert by text, WhatsApp or both. Promotional consent for those channels is required (opens in new tab) and can’t be made optional, and the form has to carry the required disclosure language. Email consent on the same form is an optional checkbox.

Our guide to SMS for ecommerce covers the federal consent and carrier rules behind those requirements.

Run email and text in one Klaviyo back in stock flow. After the back in stock delay, add a conditional split on “If someone can or cannot receive marketing”, set to cannot receive text message marketing. The condition is worded in the negative, so the text goes on the No path, to people who can receive it, and the email goes on the Yes path.

Keep it to one or two texts, and add the product name and product URL catalog tags so the link goes straight to the item. Quiet hours can hold a text even after the product is restocked. On a short run of units, the email can sell through the stock before the delayed text lands.

Shopify’s own tool for this moment is Shopify Flow. Its “Product variant back in stock” (opens in new tab) trigger starts a workflow when a variant’s inventory goes from 0 or less to 1 or more, and it needs inventory tracking turned on. Draft orders don’t change available inventory until they’re converted, so they don’t fire it.

Shopify added that trigger in August 2023 (opens in new tab), alongside one for out of stock, with automatically publishing a product when a variant returns as the example use. The trigger passes the variant to the workflow and nothing about who wanted it. That makes it a store-side tool for publishing, tagging or alerting your team, not a list of shoppers to notify.

The two can work together, with one caution. If a Flow workflow unpublishes products when they sell out, the Klaviyo back in stock button has no page to appear on, so exclude the products you’re taking signups on.

Run through these before a product you expect to sell out goes on sale:

A Klaviyo flow build with BLKDG starts with an audit of your Klaviyo account, covering the Shopify integration, the app embed, consent and the triggers and filters on every flow. We set up the back in stock form, the Shopify inventory settings and the send rules before the stock you’re waiting on arrives. If you’d like that done before your next big sale, start with a free Growth Audit.