Rename the listed columns to WooCommerce's names, or pick the field by hand in the dropdown next to each column. Make the unit in "Weight (...)" and "Length (...)" match your store settings, for example kg and cm. If every column landed in one, the file uses semicolons: save it as "CSV UTF-8 (comma delimited)" or set the delimiter under "Show advanced options".

WooCommerce CSV import: columns show "Do not import" on the mapping screen

What it means: On the "Map CSV fields to products" screen, WooCommerce picks a field for each column only when the header is exactly one of its column names, in English or in your admin language (capital letters do not matter). If a column name appears twice, only the last of them is imported. "Product Name" or "Attribute 1 value" (without the s) are not matched. Weight and size columns carry your store's unit, such as "Weight (kg)". In 11.2 and earlier the "GTIN, UPC, EAN, or ISBN" column is never matched automatically.

Find the rows in your file

WooCommerce product import

Choose file

The product CSV you are about to import into WooCommerce (Products, Import), or the one that just failed.

Your file stays on this device

It is read and converted by this page, inside your browser. Nothing from the file is uploaded, and the tool keeps working offline once the page has loaded.

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How to fix it

Rename the listed columns to WooCommerce's names, or pick the field by hand in the dropdown next to each column.
Make the unit in "Weight (...)" and "Length (...)" match your store settings, for example kg and cm.
If every column landed in one, the file uses semicolons: save it as "CSV UTF-8 (comma delimited)" or set the delimiter under "Show advanced options".

Example

A file with this problem

Type,SKU,Product Name,Regular price,Weight (lb),Attribute 1 name,Attribute 1 value
simple,MUG-1,Mug,12.00,1,Size,S

What the checker says about it

Line 1: "Product Name" is not one of WooCommerce's English column names, so unless it is the translated name in your admin language it shows as "Do not import" on the mapping screen. Rename it to a WooCommerce column name or pick a field by hand.
Line 1: The column "Weight (lb)" will not be matched automatically: WooCommerce names it after the store's unit setting, which is one of kg, g, lbs, oz. Pick the field by hand on the "Map CSV fields to products" screen, and check the numbers are in your store's unit.
Line 1: "Attribute 1 value" is not one of WooCommerce's English column names, so unless it is the translated name in your admin language it shows as "Do not import" on the mapping screen. Did you mean "Attribute 1 value(s)"? Rename it to a WooCommerce column name or pick a field by hand.

Once the listed rows are fixed, check the file again; the checker also looks for the other problems in WooCommerce's import code, so you do not trade one error for the next.

Other WooCommerce import errors

Sources

WooCommerce 11.2.2 source: class-wc-product-csv-importer-controller.php: https://github.com/woocommerce/woocommerce/blob/11.2.2/plugins/woocommerce/includes/admin/importers/class-wc-product-csv-importer-controller.php
WooCommerce: Product CSV Importer and Exporter: https://woocommerce.com/document/product-csv-importer-exporter/

Based on WooCommerce 11.2.2's import code and documentation. Not tested on a live store.