I have tried 4 different methods and always get the same error:
1. Convert excel spreadsheet to CSV by using Save as, which is in the instructions.
2. Convert excel spreadsheet to plain text file, replace tabs with commas, save with .csv extension.
3. Save file from the shopify product list to CSV file. Tried both methods, plain CSV file and Excel compatable CSV file.
4. Import file from Square. It says success but it imports 0 products.
Methods 1, 2, 3a and 3b all return the CSV file is missing error.