An invoice processing system that stores documents and moves them along is doing half the job. The other half is holding what happened: when it arrived, what it was checked against, why it stalled, who approved it and what was paid. That history is what answers questions months later, and it is the part most systems are actually bought for.
Arrival and identity
The date and channel it arrived through, the supplier, and whether this supplier and number combination has been seen. These settle payment terms, duplicate detection and most supplier queries. They are free to record at the moment of arrival and expensive to reconstruct, which is the argument for capturing at arrival rather than at processing.
What happened to it
The match result and what it was compared against. The exception reason and who resolved it. The approval with a name, a date and an amount. The coding. This is the part produced once by a person and normally discarded, and it is exactly what an auditor, a supplier dispute or a duplicate-payment argument asks about.
Versions and closure
Reissued invoices are new versions rather than new invoices, and credit notes change what is owed. Keeping versions with dates answers which one was paid against. And every invoice should end in a definite state rather than fading out of discussion, because an open list that includes items nobody is pursuing stops being trusted.
Questions people ask about invoice processing system
Is this what our accounting system does?
It records the accepted transaction. The processing system covers the stretch before that, which is where the delays and the exceptions live.
How long should the record be kept?
As long as the invoice, under your own retention obligations. The approval history is part of the record of the transaction.
What is the minimum useful version?
A record with supplier, amount, dates, status, owner and the document attached. That alone replaces a shared mailbox and a spreadsheet.