Some Etsy listings keep one quantity for the whole listing, or one quantity per option such as Size, while Shopify always counts stock for each variation. So when a Shopify sale updates one of these Etsy listings, the two shops can end up showing different numbers. The two mirror settings let Shuttle copy the result back to Shopify, so every related Shopify variation matches Etsy again.
When Shuttle mirrors updates back to Shopify
Shuttle mirrors updates back to Shopify only after a stock change on Shopify has updated an Etsy listing. This happens when the Etsy listing:
keeps its quantity on the listing, or on one option such as Size, or
has a variation whose SKU is shared by more than one Shopify variation in the same product.
Shuttle does not mirror listings with only one variation, because Etsy and Shopify already match there. Mirroring also never starts from a change made on Etsy. It only follows an update that Shuttle made to Etsy.
What Mirror quantity updates to Shopify does
Mirror quantity updates to Shopify sets each Shopify variation to the quantity its matching Etsy variation has after the update. It is on by default.
For example, say Etsy tracks stock on Size and someone buys a Small Blue shirt on Shopify. Shuttle updates the Small quantity on Etsy. With Mirror quantity updates to Shopify on, Shuttle then gives the other Small variations in Shopify, such as Small Red and Small Green, the same quantity.
When Etsy keeps one quantity for the whole listing, Shuttle sets that quantity to the lowest quantity among the Shopify variations the Etsy listing represents. Those are the Shopify variations matched to the listing's variations and, when you sync duplicate SKUs, the Shopify variations that share one of the listing's SKUs. Mirror quantity updates to Shopify then gives every Shopify variation that same number.
When the update sells out the Etsy listing, the mirror sets the Shopify variations to 0 and applies your When a product is sold out on Etsy setting, under Settings > Stock Syncer > Etsy → Shopify. A mirror never makes a Shopify product active.
What Mirror SKU updates to Shopify does
Mirror SKU updates to Shopify copies a SKU that Shuttle changed on Etsy back to every related Shopify variation. It is off by default.
This matters when Etsy keeps one SKU for the whole listing, or one SKU per option. In that case Shuttle gives Etsy the first Shopify SKU it finds for that listing or option. With Mirror SKU updates to Shopify on, Shuttle then writes that same SKU onto every Shopify variation that belongs to that listing or option.
Mirror SKU updates to Shopify only works when Sync product SKU changes between platforms is also on. That setting is under Settings > Stock Syncer > General, in the Sync product SKUs section.
Sometimes Etsy will not take new SKUs on a listing whose variations share their stock. Then the SKUs on Etsy stay as they were, and Shuttle does not copy any SKU to Shopify, whichever mirror settings are on.
Should you turn the mirror settings on?
Turn the mirror settings on if your Shopify variations should always show exactly the same quantities and SKUs as Etsy.
Leave them off if your Shopify variations need different quantities or different SKUs from each other. For example, you might count stock for each color in Shopify but only for each size on Etsy. Mirroring would overwrite those separate Shopify values with the Etsy value.
Turn on mirroring
Each mirror setting has a short note on the page that says when it applies:
Mirror quantity updates to Shopify: "Applies only when Etsy manages stock on the product or an option, or when several Shopify variations share an SKU."
Mirror SKU updates to Shopify: "Applies only when Shuttle changes SKUs on Etsy."
Go to Settings > Stock Syncer > Shopify → Etsy.
Make sure Enable syncing from Shopify to Etsy is ticked.
In When Etsy manages stock on the product or option, tick Update the Etsy product quantity from Shopify variations, Update Etsy variations based on the option that manages stock, or both.
Tick Mirror quantity updates to Shopify, Mirror SKU updates to Shopify, or both.
Click Save.
To use the Shopify → Etsy stock settings, you need the Growth plan or higher.