How to Sync Shopify and Amazon Inventory Automatically

Why Shopify and Amazon stock drifts apart

Both platforms track inventory well — for their own sales. That's the whole problem. Shopify deducts a unit when someone buys on your store. Amazon deducts a unit when someone buys on Amazon. Neither tells the other.

So if you list 15 units in both places, you're not offering 15 — you're offering 30, backed by 15 real units. Sell 8 on Shopify and Amazon still shows 15 available. The gap between the two counters is where overselling lives, and on a busy week it only widens.

The manual method (and where it runs out)

With no software you keep the two in line by hand. Every Amazon sale, you open Shopify and drop that variant's quantity. Every Shopify sale, you do the reverse in Amazon Seller Central. Some sellers instead split stock — list 8 units on Shopify, 7 on Amazon — so neither can oversell.

Both work at a handful of orders a day. Both fail as you grow. Manual updates lag reality the moment orders overlap, and split stock leaves you cancelling orders on one channel while sitting on unsold units on the other. It's admin that scales with your sales — the wrong thing to be doing more of as you succeed.

The step that makes sync possible: matching SKUs

Any tool that syncs stock has to know your Shopify listing and your Amazon listing are the same physical product. That link is the SKU. On Shopify it's the SKU field on each product variant; on Amazon it's the seller SKU set when you create or edit a listing.

Make them identical — BLU-TEE-M on Shopify and BLU-TEE-M on Amazon — for every product and every variant. Mismatched SKUs are the single most common reason sync setups fail. If you're tidying SKUs anyway, our note on adding SKUs and barcodes to listings covers doing it cleanly.

Amazon's own integration vs a dedicated tool

Amazon offers a Shopify sales channel that pushes listings and pulls orders. It's useful, but limited: it's built around getting Shopify products onto Amazon, its stock handling is one-directional and it leans US-centric. If Amazon is your source of truth and Shopify a shopfront, it can be enough.

The moment you have more than two channels— add eBay, Etsy or TikTok Shop — or you want one central stock figure that's authoritative regardless of where a sale happens, you've outgrown it. A dedicated multi-channel inventory tool holds the master quantity and treats every channel, Shopify and Amazon included, as an equal spoke.

The real fix: one central stock figure

The reliable setup is to stop letting each platform keep its own count and instead hold one central quantity that software pushes everywhere. When a sale lands on either channel, the system:

1. Detects the sale on Shopify or Amazon immediately
2. Deducts the unit from your single central stock figure
3. Pushes the new number to the other channel — and any others — in real time

Salync connects both Shopify and Amazon and syncs stock in real time, matched on SKU. Sell on Shopify and your Amazon quantity drops within seconds, and vice versa — so the two counters can't drift apart and you never sell a unit twice. It's the same engine behind syncing eBay and Amazon; adding Shopify is just another spoke.

Setting it up: the short version

1. Match your SKUs across Shopify variants and Amazon listings.
2. Connect both channels to your inventory tool (OAuth for Shopify, Seller Central authorisation for Amazon).
3. Set your true stock as the central figure — one honest count per SKU.
4. Turn on real-time sync and test with one product: buy it on Shopify, watch Amazon drop.
5. Add a safety buffer so listings go dark a unit or two before zero.

The bottom line

Shopify and Amazon each count only their own sales, so their stock inevitably drifts and eventually oversells. You can hold the line by hand at low volume, but it's admin that grows with your success. Match your SKUs, put one central stock figure in charge, and let real-time sync keep both channels honest — then add the next channel without changing a thing.