Product & Inventory Rules

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Back-in-Stock subscriptions operate at the variant level — a customer subscribes to a specific size, color, or option combination of a product, not to the product as a whole. The module’s eligibility rules are also applied at the variant level, based on the variant’s inventory_quantity value in Shopify. Understanding how these rules work ensures the widget appears where it should and notifications fire when they should.

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What this covers

• Why subscriptions are per variant, not per product
• How inventory_quantity = 0 controls widget eligibility
• Per-variant subscription limits
• Multi-variant and multi-product subscription behavior
• Edge cases in inventory management

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Subscriptions are per variant

When a customer submits their WhatsApp number through the Back-in-Stock widget, Galantis records the subscription against the specific variant they have selected — not against the parent product. The subscription record stores the variant’s selected_options (e.g., Size: M, Color: Blue) to identify exactly which combination the customer is waiting for. This means:

• A customer subscribed to Size: M, Color: Blue will only receive a notification when that exact variant is restocked
• If Size: L, Color: Blue restocks, their subscription is not triggered — it is a different variant
• A customer who wants notifications for multiple variants must subscribe separately to each one

This per-variant precision is the correct behavior — a customer waiting for a specific size does not want to be notified that a different size is available, as that does not solve their problem.

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Widget eligibility: inventory_quantity = 0

The subscription widget only appears on a product page when the currently selected variant has inventory_quantity = 0 in Shopify. This is evaluated client-side when the customer selects a variant on the product page. When a customer switches between variants on a product page, the widget shows or hides dynamically based on the selected variant’s inventory. A product page where some variants are in stock and others are out of stock will show the widget only for the out-of-stock selections.

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Subscription limits

Galantis supports configurable subscription limits per product and per variant. These limits control how many active subscriptions can exist for a given product or variant at any one time. Why limits matter: For high-demand products, an unlimited subscription list can create notification volume that exceeds your credit balance or overwhelms a limited restock quantity. Setting a per-variant limit ensures the notification list stays proportionate to the inventory you can fulfill. Subscription limits per product and per variant are configurable in the Galantis dashboard.

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Multi-variant subscriptions

A customer can hold multiple active subscriptions simultaneously — across different variants of the same product and across completely different products. Each subscription is a distinct record and is evaluated independently:

• A customer waiting for Size: S and Size: M of the same product has two separate subscriptions
• When Size: S restocks, only the Size: S subscription triggers — Size: M remains ACTIVE until that variant restocks
• A customer subscribed to variants across three different products will receive up to three separate notifications as each variant restocks, governed by the frequency cap on the automation

There is no enforced limit on how many subscriptions a single customer can hold. Frequency caps on the Back-in-Stock automation control how often a customer can receive notifications within a given time window, regardless of how many active subscriptions they hold. See Automations — Frequency Caps.

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Inventory quantity edge cases

Partial restocks — If a variant is restocked with a quantity lower than the number of active subscribers, all subscribers still receive notifications. Galantis does not check whether the restocked quantity is sufficient to fulfill all subscribers — the notification pipeline fires for all ACTIVE subscriptions regardless of restock volume. Urgency language in the notification template (“Limited stock — get yours now”) reflects the genuine scarcity without Galantis needing to manage allocation. Rapid inventory fluctuation — A variant that restocks and immediately sells out before all notifications are dispatched still triggers the full notification batch. Customers who click the link in their notification may find the product out of stock again. This is expected behavior — the notification is accurate at the moment of dispatch. Inventory adjustments that do not represent a true restock — An inventory correction that moves a variant from 0 to a positive number — for example, a merchant correcting an erroneous zero-inventory entry — will trigger the Back-in-Stock pipeline just as a genuine restock would. Galantis cannot distinguish between a correction and a genuine restock from the webhook payload alone. If inventory corrections are common in your workflow, be aware that they will fire notifications to subscribers. Inventory tracking disabled — If a product in Shopify has inventory tracking disabled, Shopify does not report an inventory_quantity for its variants. In this case, the widget will not appear (since Galantis cannot confirm inventory_quantity = 0) and the restock trigger cannot fire. Enable inventory tracking in Shopify for any product you want to use with Back-in-Stock.

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Related guides

• Subscription Lifecycle — How subscription status controls notification eligibility
• Notification Logic — How the restock detection pipeline uses inventory data
• Variants & Pricing — How Galantis stores variant-level inventory data from Shopify
• Automations — Frequency Caps — Controlling notification frequency for customers with multiple subscriptions