Here's another example:

Sales tax is Liability, not Revenue, to a business. If you are running a food takeout operation (as was typical during the worst of the pandemic), you might get paid only by credit card, with tips and taxes. We had a business that worked twice a week out of a rented kitchen; they took orders up to 4pm the day before, for delivery the next day, and you paid by credit card on the web site.

That means everything they got will be on 1099-K. But at least 1/3 is tips and taxes, so the Gross Revenue and the 1099-K won't match. But the payroll and sales tax reporting supports the difference.