How does “Bills already in Xero” work on the Proformas page?

This door looks at each company's open advances and at the bills already in Xero that could be their invoice — the same amount, a larger bill the advance was a deposit on, a shared reference. A line whose bill still has money due is Ready to post: pick the invoice and Post payment, or tick several and post them together, and Saral pays the bill from the proforma account for the smaller of what is left of the advance and what is due, dated the day the advance was paid, so debit and credit on the account fall on the same day. On a deposit the rest of the bill stays due for the next run. Paid twice? means the bill was already paid another way while the advance still sits on the account; posting cannot fix that, so the supplier owes a refund or credit, and the line leaves the list from its menu once that is done. Where: Proformas (/accounts/proformas).