Enabling the "Update Quantity for Duplicate SKUs" option in Shuttle means that when the quantity of a specific SKU is updated, Shuttle automatically updates all other variations sharing that same SKU.
Syncing duplicate SKUs is important because multiple variations often share the same SKU if they're intended to represent the same physical inventory item across your platforms.
In these scenarios, variations usually have identical stock levels, and when one variation's quantity changes, it's important that all variations with the same SKU update as well.
Example:
Let's say you have an Etsy product with three variations, each with the SKUs AAA, BBB, and CCC.
On Shopify, instead of having one product with multiple variations, you've created three separate products, each corresponding to one of these SKUs (AAA, BBB, and CCC).
Additionally, you sell a kit on Etsy, and one of its variations also has the SKU BBB.
With duplicate SKU syncing enabled, when the BBB variation sells on Etsy, Shuttle automatically updates:
The quantity of the Shopify product with SKU
BBBThe quantity of the kit variation on Etsy with SKU
BBB
Behind the scenes, Shuttle scans your entire Etsy and Shopify inventory, updating any variations with the matching SKU (BBB).
Note: To prevent misuse, Shuttle limits duplicate SKU syncing to a maximum of 10 products per platform.