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How to notify a customer when a product is back in stock?

Increase average order value with a post-purchase recommendation on Shopify or another CMS.

Back in Stock is an automation that automatically notifies your customers on WhatsApp as soon as a product they were waiting for comes back in stock.

In practice: a customer lands on an out-of-stock product page, clicks a "Notify me on WhatsApp" button, enters their phone number, then receives a personalized notification the day the product (or the specific variant: size, color, etc.) becomes available again.

This is a particularly powerful flow because it captures a purchase intent that already exists: the customer wanted this product, all you need to do is notify them at the right moment.

Observed results 📈

On WhatsApp, Back in Stock shows significantly higher performance than traditional channels:

90% average open rate

13% average conversion rate

Concrete examples 💡

To illustrate, here's how Back in Stock adapts to different types of stores:

Figaret (Ready-to-wear)

👉 The button is integrated directly into the brand's style, in the same spot as the purchase button.

Motus Boutique (Ready-to-wear)

Nars (Beauty, Cosmetics)

💡These examples show that Back in Stock works just as well on highly seasonal products (fashion) as on high-turnover items (beauty).

1. Setting up the native Back in Stock button on your store

Before you start:

  • You need a Shopify site.

  • You need at least one out-of-stock product published on your site, or, failing that, be able to mark one as out of stock for the duration of the setup (activation takes about 3 minutes).

There are 2 automatic integration methods depending on the desired button style, plus a manual integration for highly customized sites.

Method 1: Shopify Block

  1. From your Shopify theme, add the Wax Back in Stock block to your product page template.

  2. Position it where you want (usually under the purchase button).

  3. Save: the button appears automatically when the variant is out of stock.

Method 2: WAX Widget (floating button)

  1. Enable the floating widget from the WAX app settings.

  2. Customize its position and text.

  3. The widget automatically displays on out-of-stock product pages.

Method 3: Manual integration

Use this if your site is highly customized. Pass these instructions to your developer:

  1. Enable the Shopify App Embed Wax Back in stock extension and, in the extension settings, enable "Enable manual integration".

  2. Build a button near the location and style of the purchase or back-in-stock alert button, with a WhatsApp-related label (e.g., "Notify me on WhatsApp").

  3. Make this button visible only if the variant is out of stock, and hidden if it's available.

  4. On click, call the globally accessible method:

waxOpenBackInStockModal(variantId)

This modal is entirely generated by WAX: it handles the display, entry, and validation of the phone number itself. The developer has nothing else to build once this call is made.

Method 4: without a native block, via an event (non-Shopify site or incompatible theme)

If your Shopify theme doesn't allow adding the native block or widget (theme too customized), or if your site isn't on Shopify, you can replicate the same journey using an event instead of the native integration:

  1. Build the button and collection form yourself on your product page: a field for the customer's phone number, shown only when the product (or variant) is out of stock.

  2. When the form is submitted, save the customer in your own system (CRM or database), on a dedicated list (e.g. "Waiting for restock"). At this stage, nothing is sent to WAX yet: the waitlist is managed entirely on your side.

  3. Set up a flow in WAX triggered by an API call, which sends the WhatsApp notification directly to the contact passed in that call.

  4. As soon as the variant is back in stock, it's your system (CRM or platform) that must call the WAX API for each contact waiting on that product, passing their phone number along with the product information. Depending on how personalized you want the message to be, this call can include product_name, product_image, or variant_image, and at minimum, the link to the product page. It's this call that triggers the immediate notification. If your tool can't make this call easily, a no-code tool like Make or Zapier can bridge the gap.

💡This method requires technical integration (webhooks, events): plan for support from your developer or CRM to set it up, or contact our support team for assistance.

2. Configuring the use case in WAX

The steps below describe the setup for Methods 1, 2, and 3 (native Shopify block, widget, or WAX modal), where WAX automatically detects the restock on Shopify and manages the waitlist itself. For Method 4 (without a native block, via an API call), the WAX flow only needs an API trigger: there's no waitlist to create on the WAX side, since your system manages it and calls WAX only when it's time to notify each contact.

Once the button is in place, you need to create a flow that will trigger the message at the right time.

  1. Go to your flow library in WAX → This is the starting point for setting up your automations.

  2. Add the Back in Stock template → Pre-configured to trigger the notification at the right time.

  3. Customize your message → Add variables to send the right information to each customer:

    • {{product_title}} → the product name as it appears on Shopify

    • {{variant_id}} → useful for specifying a variant (size, color, etc.)

    • Image and link variables → to display a visual + redirect to the product page

    👉 Result: each customer receives a 100% personalized notification, with the right product, the right variant, and the right link.

  4. Test the flow before activating it for all your customers: mark a test product as out of stock, sign up yourself via the "Notify me on WhatsApp" button, then put that product back in stock on Shopify. Check that you receive the expected WhatsApp notification (text, image, link) before activating the flow across your entire catalog.

  5. Activate the flow for all your contacts → As soon as a variant comes back in stock, the send goes out automatically.

Once the button is in place and the flow is activated, the journey works end-to-end without any action on your part: a customer clicks "Notify me on WhatsApp" on an out-of-stock product page, enters their number, then receives a personalized WhatsApp notification (product name, variant, image, and direct link to the product page) as soon as that variant is back in stock on Shopify.

FAQ ❓

How do I download our Back in Stock app?

If you already have the WAX app installed on your Shopify store, the Back in Stock embed app is included by default: there's nothing to download.

What if the product comes back in stock several times?

Only one message is sent per sign-up. If the product goes out of stock again and comes back, the customer needs to sign up again to receive a new alert.

Can the message be customized?

Yes. All variables related to the product and its variant are available in the flow, allowing full customization of the message.

300 customers signed up for my Back in Stock alert, my product is back in stock but only for 20 units. Can I notify only the first 20 who signed up?

No, the message is sent to all subscribers.

Can I see the list of subscribers?

Yes, on request from your CSM.

The button doesn't integrate well with my product page, what should I do?

Follow the written or video guide above first. If your Shopify theme is highly customized, manual integration will be needed (see section 1, Method 3).

What languages are available for the popup where the customer chooses their variant and enters their number?

Currently: French and English only. If your site is in another language, contact us.

In what cases might this not work?

If your store is highly customized with specific blocks, manual integration will be needed (see section 1, Method 3).

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