Match the four inventory fields by SKU number
Mercari Shops inventory updates require Product ID plus matching fields such as `SKU1_ID`, `SKU1_現在の在庫数`, `SKU1_増減フラグ`, and `SKU1_在庫増減数`. SKU2–SKU10 follow the same numbered relationship.
The checker pairs fields by SKU number rather than by their left-to-right position, so a missing intermediate column cannot silently connect the wrong SKU.
Do not type +3 or -2 in the quantity field
Delta flag `1` means plus and `2` means minus. The delta quantity itself is entered as a positive integer without a sign.
To subtract 3, use flag 2 with quantity 3.
Current stock is only a snapshot
The current-stock field reflects the exported point in time. Orders or individual edits while you work on the CSV can change live stock before upload.
This is especially important for decreases, because a valid-looking file can become impossible if live stock falls during editing.
How to read the result
ERROR covers missing Product/SKU IDs, incomplete field sets, invalid flags, or invalid positive quantities. Even with zero errors, the checker cannot remove the timing gap to live stock.
For a broader file check, also use the Mercari Shops bulk-update CSV checker.