How to implement these actions in 1C?

Question

1C

If the user has not specified a vendor contract that is being paid, the document must allocate the payment amount starting with the contracts with the earliest due date.
If the payment exceeds the amount owed to the supplier under the contract chosen by the user, then we overpaid, and the difference between the amount of payment and the amount owed to the supplier is already a debt to us. Then the overpayment should be debited to the account for recording advances issued (account "Accounts", which is accounted for by organizations).
How to do this, provided that the Agreement is a reference book with the Payment Date attribute?

Answer 1

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