You clarified: "The S Corp was on a cash basis. They did not pay the payroll liability until after the sale occurred."

Paying those liabilities is your Banking date; not the expense date.

The expense is not incurred when paid, for payroll. The tax expense is owed because of the payroll date. That's why it is carried as a liability, and paying any liability is not expense.

Nothing changed for these activities; your client had employee funds on hand, showing those values as a liability, and has matching/similar employer tax expense along with the gross wage expense for that payroll date. That's Cash Basis payroll.

Accrual Basis payroll expense would be based on some accrual date, not on each pay date.