Shopify and Amazon records can refer to different quantities even when they describe the same product. Start by matching identifiers and definitions before comparing totals.
Create the mapping
- Match the storefront variant to the seller SKU and marketplace. Check pack size and bundle contents, not just the product name.
- Record which location holds the stock and which channel may use it.
- Label each quantity by its actual meaning: physically held, available to sell, reserved or awaiting receipt.
- Keep the export time and reporting period with every file.
Amazon distinguishes fulfillable, reserved and inbound inventory. A storefront quantity should not be equated with the sum of those states without checking what it represents.
Reconcile the difference
Compare records from an appropriate shared cut-off, then list the orders, cancellations and stock movements that occurred between exports. Investigate an unmatched identifier before adjusting a quantity. Keep a note of the correction and the source record used.
If a connector is involved, document its access, mapping and error-handling responsibilities. Test a documented movement and inspect the resulting records. A working connection still needs reconciliation and a person who handles exceptions.