A Notify Me button is for the variant that is gone, not for the whole product. On a shoe or a shirt, one size can be sold out while other sizes still add to cart. SK Back In Stock's listing says the app replaces Add to Cart with Notify Me when a product or variant is sold out, using theme app blocks, and that customers can wait for a size or color.
The steps below follow the app's documented behavior, plus checks on one size in your theme. Confirm the live listing before you treat any extra screen as guaranteed.
Variant versus the whole product
If the button ignores the selected size, a shopper who wanted a 9 can end up on the waitlist for an 8 that the theme had preselected. The catalog stores both the product ID and the variant ID on every signup. Inventory events resolve to the variant whose quantity changed. The email job is targeted at that variant's waiting list.
The button's visibility follows the variant currently selected. Changing size or color shows or hides Notify Me without reloading the page. If the theme block does not expose product data, the widget can load it from the product's public JavaScript endpoint.
That is why the test is a variant test. Select a sold-out size and confirm Notify Me is available. Select an in-stock size of the same product and confirm the page still offers purchase for that size. Then go back. The catalog's intent is that only the unavailable variant collects the email.
Where the button is placed
The catalog describes two placements: a theme app block on product pages, and a global app embed. You can keep more than one configuration. Each configuration can apply to all products, to chosen collections, or to chosen products, and it can carry an exclude list. A collection target chooses which products inherit that button setup. It is not documented as a Notify Me control on collection cards.
The admin can ask Shopify whether the embed is enabled in the current theme and how many Notify Me blocks are placed on product templates. Use that check when the storefront looks unchanged after install. A block saved on an unpublished theme, or an embed left off, will not show the button to shoppers.
The button and popup sit in a closed shadow DOM, so theme CSS will not restyle them like a normal Add to Cart button. Set colors and type in the app's own controls. The signup modal is placed on the page body so a sticky gallery does not clip it.
Button, popup, and email template
The listing names a button, a popup, and email templates. The catalog lists the controls behind those three pieces. You can set button text, an icon (none, bell, email, or notification) and the icon's position, colors for background, text, border, and hover, border width and radius, font size and weight, and width and alignment.
The popup has its own title, description, field labels, placeholders, submit text, and messages for success, error, and already subscribed. You can set close behavior, width, background, radius, and overlay opacity. Write the popup so it names the action: the shopper is asking for an email when this variant is available again. Do not write a sentence that promises a text, a WhatsApp note, or a held unit. Those are not in this app's catalog.
- Button: the storefront control shoppers see on the sold-out variant.
- Popup: the email field, the consent copy you write, and the success or error message.
- Email template: subject and body with placeholders for product name, product URL, new price, and old price.
The catalog does not list a separate placeholder for variant title. The send is still per variant, so only people who joined that size or color are queued. If the product-name placeholder prints the product title alone, say the size in copy you can control, and test it with two variants so a shared template does not tell a size large subscriber that size small is back. You can send one test email to yourself before any shopper is notified.
What to test on one size
Pick one product with at least two variants. Make one variant unavailable and leave another available. Set the stock threshold to the catalog default of 1 unless you have a reason to wait for a larger receipt. A threshold of 1 means the crossing that matters is from below 1 to 1 or more.
- On the storefront, select the sold-out size and join with an inbox you can open.
- Select the in-stock size and confirm you are not shown the same sold-out signup for that size.
- Send the template test to yourself and read the subject, the product link, and any price tokens.
- Raise only the sold-out variant across the threshold. Confirm one queued alert for the address that joined that variant.
- Add more units to the variant that was already above the threshold. The catalog says that further restock does not fire another back-in-stock alert.
- Open the signup row and check the variant, the status, and, after a successful send, the notified date.
The inventory webhook queues the email. A worker sends it. A failure retries up to five times, then the job is marked permanently failed. The catalog does not publish a delivery-time promise.
What not to claim in the button copy
Do not write "We'll text you," "We'll WhatsApp you," or "Preorder now" on this button. The catalog is email, variant by variant, when quantity crosses the threshold. It does not document SMS, WhatsApp restock alerts, preorders, deposits, or a Klaviyo connection. The App Store listing tags its notifications as multi-language, but neither the listing nor the catalog says which storefront or email languages are covered. The admin screens are localized in English, German, and French. Test the shopper-facing text in your own language before you rely on it.
Do not promise a restock date in the popup. The app does not know the purchase order's arrival day. Do not promise a discount. The template can show a new price and an old price. Those values are prices, not a code you have not created.
Questions about the button
Can collection pages show Notify Me?
The documented surfaces are a product-page block and a global embed. A configuration can be limited to products in a collection. A button on the collection card is not described.
Can I brand the email?
You can edit the subject and body. The documented inserts are product name, product URL, new price, and old price. Send yourself the test and read it before a real restock.
What if only one size is gone?
Leave the product published. Shoppers who select an available size should still be able to buy. Shoppers who select the missing size should see Notify Me for that variant.
Install SK Back In Stock only after the live listing still matches this email button, and after you have tested one sold-out size on your theme.