How do I clear a proforma against the bill once it is in Xero?

On a Ready to post line pick the matched invoice and Post payment, or tick several and post them together. 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. Matches offered: the same amount, a larger bill the advance is a round share of, or a shared reference.