The receipts import ignores the invoice number and allocates each receipt using the first in, first out method, against the oldest open invoice. Clients often pay a specific invoice, so we reverse and reallocate by hand. This wastes time and causes errors on the debtor ledger and client statements.

Suggested logic:

Invoice number provided: allocate against that invoice.
No invoice number, one open invoice on the ledger matches the amount: allocate against that invoice.
No invoice number, more than one open invoice on the ledger for the same amount: allocate against the oldest of them, using the first in, first out method. Use this method only when the ledger holds more than one invoice for the same amount.
No invoice number, no match: leave the receipt unallocated on the client ledger.

Edge cases:

Invoice not found or already paid: leave unallocated and flag it.
Receipt above the invoice balance: allocate up to the balance, leave the excess unallocated.
Receipt below the balance: allocate as a part payment.

Please also add an import report showing how each receipt was allocated, and an invoice number column in the import template if one does not exist.

Benefits: allocations match remittances, fewer manual corrections, accurate aged debt and statements.