How do you keep inventory in sync across Amazon, Flipkart, Myntra and Shopify?

Updated:

Keep one stock ledger as the source of truth, and map every channel SKU to one master SKU. Reserve stock against each order when it is confirmed. Then push the available quantity back to each connected channel whenever stock changes. Most overselling happens in the gap between a sale on one channel and the update reaching the others.

If you sell on two marketplaces and your own Shopify store from one warehouse, every unit is on offer in three places at once. The sections below explain why counts drift apart, what a sync should actually update, how to fix a mismatch between system and shelf, and what to ask before choosing a tool.

Why does overselling happen when you sell on several channels?

Overselling happens when a channel shows stock that has already been sold or is not really available. The usual causes:

  • Update lag. A unit sells on Flipkart, but Amazon and the Shopify store still show it until the next stock update reaches them.
  • Manual updates. Stock is uploaded by spreadsheet once or twice a day, so every sale in between is invisible to the other channels.
  • Unmapped or duplicate SKUs. The same product has different SKU codes on each channel, and one code is not linked to the warehouse SKU.
  • Bundles and combos. A combo pack is listed as its own SKU, so selling it does not reduce the count of the single items inside it.
  • Stock that is not sellable. Damaged, returned-but-uninspected or held units are still counted as available.

Each oversold order is usually cancelled, and repeated seller-side cancellations can count against a seller's account health on the marketplace.

What does inventory sync actually update?

A useful sync pushes available-to-sell stock, not just what is on the shelf:

available to sell = on hand − reserved for open orders − held or damaged stock

So a good sync depends on three records being right: the on-hand count in the warehouse, the reservations for orders that are confirmed but not yet shipped, and any stock that has been put on hold. Bundles need one more step: the available count of a combo is limited by its scarcest component.

How often should inventory sync to Amazon, Flipkart, Myntra and Shopify?

Each marketplace sets its own limits on how often and how many stock updates it accepts through its API, so updates reach each channel within those limits rather than all at the same instant. What you can control:

  • Trigger on change. Send an update when stock moves (an order, a return, a GRN, an adjustment) rather than on a fixed daily upload.
  • Batch within limits. Group changes so each channel accepts them without throttling.
  • Watch the last units. The sync gap matters most for SKUs with only a few units left. That is where oversells cluster during sales.

When you compare tools, ask how updates are triggered and batched for each channel, and what happens when a channel rejects an update.

Why does system stock not match physical stock, and how do you fix it?

A mismatch between the system and the shelf usually comes from steps that were not recorded:

  • Items picked or moved without a scan.
  • Returns put back on the shelf before they were inspected and recorded.
  • Inbound stock shelved before the goods receipt (GRN) was posted, or posted against the wrong SKU.
  • Damaged or expired stock left in sellable bins.
  • Stock moved between bins or warehouses without a transfer record.

To fix it, count first, then fix the process. Run cycle counts on your fastest-moving and highest-value SKUs every week, rather than one full stock-take a year. Record every movement with a scan. Inspect returns before they become sellable again. Investigate repeated variances by bin and by SKU. A sync can only push the count it is given, so an accurate warehouse ledger comes before any channel sync.

Should you hold back buffer stock for each channel?

Some brands keep a small buffer, showing slightly fewer units than they hold, so that the sync gap does not cause oversells on the last units. Others ring-fence stock for a channel during a sale. Both reduce cancellations but leave some stock unsold on other channels. Decide per SKU: buffers make sense for fast sellers with few units left and little sense for slow movers.

What should you look for in an inventory sync tool in India?

Ask each vendor for evidence, not a feature list:

  1. Which channels run in production today, with real sellers, and which are only "supported".
  2. How stock updates are triggered and batched for each channel, and how failed updates are retried.
  3. How SKUs are mapped, and what happens to an order for an unmapped SKU.
  4. Whether reservations, holds and bundles are deducted before stock is pushed.
  5. Whether the sync shares a record with the warehouse, or depends on a separate WMS integration.
  6. How it connects to your ERP, and who sets up the mapping.

How does Fretron CommerceOS sync inventory across channels?

Fretron CommerceOS is order, warehouse and shipping software for Indian consumer brands, running orders, warehouse and delivery on one live record beside your ERP. There is no prebuilt ERP connector. ERP data moves through Fretron's REST API, webhooks or CSV, with the mapping set up per customer.

  • Amazon, Flipkart and your Shopify store run in production, with orders pulled and inventory published back automatically.
  • When stock changes, the available quantity is recalculated and pushed to each connected channel automatically, in batches within each channel's limits. It's designed to reduce overselling.
  • Each channel's SKUs and locations are mapped to your catalogue and warehouses; an unmapped SKU doesn't come in until you map it.
  • Stock is reserved against the order when it is confirmed and allocated.
  • Stock is held on one on-hand ledger, with reservations, batches and serial numbers recorded on it.
  • Bundles and kits are resolved against their real components.
  • A stock hold takes the held stock out of what's offered for sale.
  • Fretron CommerceOS has a Myntra (PPMP) connector for orders, inventory push, ready-to-dispatch labels and returns. It is supported but not yet in production use.
  • Meesho, Nykaa, AJIO and Tata CLiQ connectors: in progress, not available today.

Integration status as of Oct 2026.

Read more about the order management system, the full Fretron CommerceOS suite, marketplace integration, and how stock is picked once an order is allocated in warehouse order picking.

Comparing software vendors? See Unicommerce alternatives and competitors, compared.

Frequently asked questions

What is inventory sync?
Inventory sync keeps the available stock shown on each sales channel in step with the stock in your warehouse. When a unit sells, is returned or is received, the new available quantity is sent to every other channel that lists it.
What causes overselling on marketplaces?
Overselling happens when a channel still shows stock that has already sold elsewhere or is not sellable. Common causes are slow or manual stock updates, SKUs that are not mapped across channels, combo packs that don't reduce their components, and damaged or held stock counted as available.
Why does system stock not match physical stock?
Usually because a movement was not recorded: an unscanned pick, a return shelved before inspection, a GRN posted late or against the wrong SKU, or stock moved between bins without a transfer. Regular cycle counts and scanning every movement fix most of it.
How does Fretron CommerceOS push stock updates to channels?
When stock changes, the available quantity is recalculated and pushed to each connected channel automatically, in batches within each channel's limits. It's designed to reduce overselling.
Which channels does Fretron CommerceOS sync inventory with?
Amazon, Flipkart and your Shopify store run in production, with orders pulled and inventory published back automatically. Fretron CommerceOS has a Myntra (PPMP) connector for orders, inventory push, ready-to-dispatch labels and returns. It is supported but not yet in production use.
Does Fretron CommerceOS count bundles and held stock correctly?
Bundles and kits are resolved against their real components. A stock hold takes the held stock out of what's offered for sale.

See inventory sync in Fretron CommerceOS.

Bring your channel list and a few SKUs with combo packs to the demo, and we will walk through how their stock would be mapped, reserved and pushed to the connected channels.

Book a demo →