GNIZDO

How to sync inventory between Shopify and Amazon

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For most Shopify sellers connecting Amazon today, Shopify Marketplace Connect is the first official path to check. It can connect Amazon, link marketplace listings to Shopify products, and sync orders and inventory.

The part that needs judgment is not the button that turns sync on. It is deciding which Shopify variant and Amazon offer represent the same sellable unit, and whether the quantity belongs to merchant-fulfilled stock, FBA stock, or a mixed setup.

Editorial illustration of marketplace channels connected to a warehouse stock source and a parcel.

Direct answer

If Shopify is your operating catalog and Amazon is the marketplace, Shopify Marketplace Connect can provide the connection for supported Amazon accounts. If another ERP, WMS, or inventory system owns the sellable quantity, keep that ownership explicit and let only one path feed the quantity into the Shopify-to-Amazon workflow.

Do not start by forcing Shopify and Amazon to show the same number. First determine whether they are supposed to represent the same inventory pool.

Decide whether the Amazon offer is FBM or FBA

FBM (Fulfilled by Merchant) can share a merchant-controlled stock pool with Shopify. A Shopify sale and an Amazon FBM sale may therefore consume the same units, so delay between the two channels matters.

FBA (Fulfillment by Amazon) is different. Those units are stored in Amazon fulfillment centers. FBA quantity should not be treated as automatically equal to the merchant-fulfilled quantity in Shopify. Marketplace Connect also supports mixed Amazon fulfillment workflows, so document which pool each offer is using before comparing numbers.

Understand what Amazon quantity belongs to

Amazon separates shared catalog content from the seller's offer. The product listing contains shared product information; the seller's offer carries seller-specific price, inventory quantity, and fulfillment options.

That distinction matters during diagnosis. A product can be correctly linked to the Amazon catalog while the seller offer still has the wrong quantity or fulfillment configuration.

Set up the inventory path

Where multichannel drift happensBoth channels sell from one stock pool, but each keeps its own reported quantity until an update reaches it.
Channel A Shows 1

Records the sale and lowers its own count.

Updated

Shared physical inventory 1 unit left

The stock both channels sell from.

Update or observation delayed

Channel B Still shows 2

Keeps its earlier value until the change arrives.

  1. StartsA sale or stock change is recorded on Channel A.
  2. Drift windowChannel B still offers the earlier quantity. A queue, retry, rate limit, or failed write keeps it open longer.
  3. EndsChannel B is updated, and a fresh observation shows the new value.
  1. 01

    Choose the inventory pool

    For every Shopify variant you want to sell on Amazon, state whether Amazon consumes the same merchant-held stock, a separate FBA pool, or another allocated quantity.

  2. 02

    Link the correct sellable unit

    Link the Shopify variant to the corresponding Amazon offer. Existing marketplace listings can be linked in Marketplace Connect; suggested matches are a starting point, not a reason to skip verification.

  3. 03

    Choose one upstream stock authority

    Decide where the sellable merchant-held quantity is edited: Shopify itself or an upstream inventory system. Avoid two independent systems writing competing values into the same pool.

  4. 04

    Use one marketplace connector

    Shopify explicitly recommends having only one marketplace connector connected at a time to avoid data conflicts. Remove an old connector before making a new one authoritative.

  5. 05

    Test one low-risk SKU

    Make a controlled stock adjustment on one linked item, record the time, and verify the resulting Shopify quantity, Amazon offer quantity, and fulfillment mode. Do this before enabling a large catalog.

  6. 06

    Measure the delay near zero stock

    Record how long it takes the other channel to reflect a sale or adjustment. A workflow that is acceptable at 50 units may still expose the last one or two units to overselling.

When Shopify and Amazon still disagree

  • Check fulfillment first. An FBA quantity and a Shopify merchant-held quantity may describe different stock pools.
  • Check the link. The Amazon offer may be linked to the wrong Shopify variant or may not be linked at all.
  • Check for a second writer. Another connector, ERP, feed, or direct marketplace edit can overwrite the quantity after a successful sync.
  • Check order import and timing. A completed connector job does not by itself prove that the current quantities agree.
  • Check low-stock rules. Buffers or channel-specific allocation can make different values intentional.

Verification checklist

  • Shopify variant and Amazon offer represent the same sellable unit.
  • FBM, FBA, or mixed fulfillment is documented for the offer.
  • One system owns the merchant-held sellable quantity.
  • Only one marketplace connector is responsible for the path.
  • A controlled quantity change reaches the expected Amazon offer.
  • The normal delay is known, especially for low-stock items.

Where GNIZDO fits

GNIZDO is not the Shopify-to-Amazon synchronization engine and does not currently provide an Amazon integration. Its role is independent inventory evidence for supported connected channels: what a channel reported, when it was observed, whether the evidence is fresh, and where confirmed shared items disagree.

Shopify is currently implemented as a read-only GNIZDO runtime, but public merchant connection remains gated until the GNIZDO Shopify App Store listing is published.

Sources and checked date

Platform facts on this page were checked October 4, 2026.