Enable SKU inventory cart validation

Cart validation prevents a shopper from exceeding the available stock by spreading the same SKU across multiple cart lines.

Prepare existing products

For an existing store, open 424 Inventory Sync → Inventory Sync and select Set Metafields under Set Metafields for Cart Validation. This initializes the synced inventory data used by the validation function.

Run this once for existing SKU groups. Ongoing inventory sync keeps the values updated afterward.

Add the checkout rule

1. In Shopify admin, go to Settings → Checkout.
2. Scroll to the checkout rules area and select Add rule.
3. Choose SKU Inventory Validation.
4. Save the rule.
5. Turn the rule on.

What shoppers see

The rule groups cart quantities by SKU. If their combined requested quantity exceeds the available synced inventory, checkout asks them to reduce the quantity and states how many items are available.

If inventory data is unavailable for a SKU, validation skips that group rather than blocking the entire cart.

Test the rule

Add two products or variants sharing one SKU to the cart. Confirm that a combined quantity at or below available stock proceeds and a quantity above it produces the inventory message.