In some cases, the total gross payment amount on Form 1099-K may not belong to your business. If the cashback was not part of your business, you can exclude that amount when you enter the 1099-K and only enter the receipts for your business. Keep records in the unlikely event you receive an inquiry.
If it is part of your business, report the full amount of the 1099-K and then use the Rebates and Refunds income category under Self-Employment income as a positive number. You won't see this option until after you have entered some kind of self-employment income. See image below.
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