How does “From the list into a payment run” work on the Bills page?

Only an approved bill with something still outstanding can be ticked; the tick box says why otherwise. Ticked bills are added to the open draft payment run (or a new one) from the header, or put on hold with a reason. The run itself — the bank file, approval, posting to Xero — is Payment Runs' work; this page just feeds it. Credit notes are shown on their own tinted rows and never go into a run. Where: Bills (/accounts/purchase).