Resetting Your Square Catalogue

Delete all items in your Square catalogue in preparation for uploading your product SKUs to Square.

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Follow Square's instructions for exporting your items library, choosing Excel (.xlsx) as the export format. Wait until the Excel file has been downloaded.
Open the newly-downloaded Excel file in the spreadsheet editor of your choice. Delete all but the first record after the header, as Square will not allow you to upload an empty spreadsheet. Save your edited spreadsheet with the single data record to a CSV file. Use the default CSV export settings.
Follow Square's instructions for importing your library, choosing the Replace Item Library option and using the CSV file you created as part of the previous step.
There will now be one item remaining in your Square Items Library. Delete it.
There are now no items in your Square catalogue.