the sold-out size comes back, and the customer hears it on WhatsApp.
Back-in-stock alerts is a form on the page of a sold-out Shopify variant: the shopper leaves their name and WhatsApp number and, when stock returns, gets a message with the cart already built. It's included in all four plans of the heysteff: WhatsApp Marketing app (from 0 USD/month, 0.08 to 0.15 USD per alert) and in Pro and Max.
heysteff is an AI platform for customer support and sales across WhatsApp, Instagram, Messenger, SMS, Gmail and Shopify; Steff is the AI agent that runs it. In fashion and accessories the whole product rarely sells out: size M or the black color does. The shopper who lands on that page leaves and doesn't come back. With this module they leave their number in ten seconds and you write to them right when they can buy.
How it works
You add the "Back in stock alert" block to the product page from the theme editor, or turn on the app embed that places it on every product page. When someone picks a sold-out variant, the form appears below the button with name, country code and phone. The country comes from the store, and an invalid number is rejected instead of being stored as a guess.
heysteff checks the stock of the variants people are waiting for every 10 minutes. When one comes back, it writes to each subscriber, oldest first, with their name, the product and variant, and a link that opens the cart with that variant already in it. The product name comes from Shopify, never from what the browser sent.
If a customer asks on WhatsApp about something sold out, Steff can also sign them up, using the phone number of that same conversation.
The module in numbers
| Item | Value |
|---|---|
| Subscription unit | The variant (size, color), not the whole product |
| Stock check | Every 10 minutes |
| Subscription length | 90 days by default, configurable from 1 to 365 |
| Sign-ups per phone | Up to 3 per day |
| Demand alert to your team | When a sold-out variant reaches 20 subscribers (configurable) |
| Group message | Up to 5,000 subscribers per send |
| Channel | WhatsApp only, from your own number |
It only alerts when the item can really be bought
"Back" means Shopify sells it again, the product is active and the variant isn't set to keep selling without stock. A variant your store lets people buy while sold out doesn't show the form, and one that's on heysteff pre-order doesn't alert until you confirm it arrived. If the variant sells out again before the message goes out, the alert is kept for next time: saying "it's back" about something sold out is worse than not writing.
heysteff doesn't ask for permission to read your inventory, so it knows the variant is back, but not how many units there are.
From your WhatsApp, with an approved template or by QR
The alert always goes out from your own number, never from heysteff's shared number: it's a sales message and Meta treats it as marketing. On the official API it uses an approved marketing template with three variables (name, product and link); heysteff offers a suggested one. By QR it goes as free text, at a slow pace that shares a daily budget with cart recovery so your number isn't put at risk.
It respects your quiet hours. Anyone who replies STOP stops receiving alerts and all their subscriptions are closed.
What you see in the app
The section shows the period's numbers, what your customers are waiting for most, the subscriber list with filters and CSV export, the send history and a button to message everyone waiting for a variant at once, for example to tell them when it arrives. Since the alert is a campaign, its clicks and sales show up in campaign results.
Frequently asked questions
How do I send a WhatsApp alert when a Shopify product is back in stock?
With heysteff's back-in-stock alerts module: you add its block to the product page, the shopper leaves their WhatsApp number on the sold-out variant, and heysteff writes to them with the cart built when Shopify sells it again. Stock is checked every 10 minutes.
How much do back-in-stock WhatsApp alerts cost?
In the heysteff: WhatsApp Marketing app, each alert counts as one message: 0.15 USD on Free, 0.12 on Starter (19 USD/month), 0.10 on Growth (59 USD/month) and 0.08 on Pro (99 USD/month). On the web plans it's included from Pro (299 USD/month). What Meta charges for the template is separate.
Can I alert by size or color instead of the whole product?
Yes, and that's the only way: subscriptions are per variant. Whoever waits for size M gets the size M alert; whoever waits for black gets nothing when blue comes back.
Can I use heysteff's WhatsApp number for the alerts?
No. The alert is a sales message and only goes out from the merchant's own WhatsApp, on the official API or by QR. Without your own number connected, the module can't be switched on.
What happens if the product sells out again before the alert?
The alert doesn't go out. heysteff checks stock right before writing and, if the variant sold out again, the subscription goes back to waiting without using up the alert.
Can I export the list of people waiting for a product?
Yes. The subscriber list can be filtered and exported to CSV with the same filters, and you can also message everyone waiting for a variant at once.
◆ next step
Don't lose the shopper who came for a sold-out size: tell them on WhatsApp the day it's back.
Also relevant: heysteff: WhatsApp Marketing, storefront assistant, repeat purchase reminders, AI for fashion brands and pricing.