A commission is "Pending" for the refund window set in Program settings, 14 days by default, in case the order gets refunded. After that it needs approving before it can be paid.
On Affiliates, if there are pending commissions old enough, a banner offers to approve every pending commission older than the refund window. Click "Approve" to approve all of them at once.
On one affiliate’s page, click "Approve" in the Commissions card to approve just theirs.
The "Ready to pay" figure on both pages is approved commissions minus anything taken back from refunded orders since.