I am customizing OpenERP for a client. I have a situation where my client needs to pay a vendor in advance but the exact invoice amount is not yet confirmed.

The approach I am thinking of, is to create a supplier invoice (account.invoice and corresponding lines), and invoke the payment wizard on that invoice. I am thinking of overriding any function that prevents payment on draft invoices. Later on when the amounts are final, I can make the changes in account.invoice and lines records.

1. What adverse accounting/reconciliation effects will this approach have, if any?
2. Is there any other, better way of doing this?

EDIT: I tried this approach. The draft invoice gets created and i am able to process a payment. But it doesn't show the payment in the payments section of the invoice. The payment is stored as journal entries / account moves only.

After validating invoice, I try to do manual reconcile... I select the invoice line and the payment line in the reconcile screen and do partial reconcile. Now when I go to the invoice payments section, it shows the payment, but it also brings along many other unrelated journal entries thus upsetting the paid total balance.

Please advise.

Thanks