Gather the supporting records
Group bank and card statements, invoices, receipts and contracts by period. Preserve the transaction purpose and service period, not just the payment date.
Separate open questions
Do not guess a missing purpose, counterparty or period. Keep an open-items list and tell your contact about substantial purchases or new contracts.
Retain originals and electronic records
The National Tax Agency describes corporate record-retention duties and exceptions. Paper and electronic transactions can have different requirements. Keep original data and confirm the applicable storage method with your tax accountant.