An invoice is a bill that a seller issues to a buyer (most often a foreign one) describing the goods or service, the amount, the currency and the payment details.
In plain words
In international practice the invoice is the main document for payment and for documenting a deal. It normally states the number and date, the details of both parties, a description, quantity and price, the currency, the payment terms and deadline, and the recipient’s IBAN and SWIFT. A bank that credits foreign-currency income may ask for the invoice and the contract to understand the purpose of the payment. In Ukraine a similar document is called a payment invoice (rakhunok-faktura); the invoice is its international counterpart.
Example. A sole-proprietor developer issues a Canadian client an invoice for USD 2,000: number INV-2026-014, description “Module development”, the IBAN and SWIFT of their bank, payment due in 14 days (illustrative data).