Manual Check Vouchers Won't Process

We have a few vouchers that were paid by manual check. When we try to run AP20 Process Vouchers, we can see the vouchers when we click View Vouchers, but they do not process when we run the report. Why?

Vouchers with a "pay by" setting of Manual Check in voucher entry will NOT be processed by the Process Vouchers report. Payments for these vouchers must be manually added on the Payments tab of the voucher.