What is an invoice?
An invoice records what was supplied, how much is owed and when payment is due. It is a request for payment—not proof that payment has arrived.
What an invoice does
An invoice turns an agreed sale into a clear payment request. It identifies the seller and customer, itemises the work or goods, shows the amount due and gives the customer the information needed to approve and pay it.
It also creates a record both sides can match to the job, quote, purchase order or account entry.
When to issue one
Issue the invoice at the point agreed with the customer: on completion, at a milestone, on delivery or on a recurring date. Sending promptly removes avoidable delay from the payment clock.
What an invoice is not
A quote proposes a price before work begins. A receipt confirms money has already been received. A proforma invoice can present expected charges in advance but is not automatically the final accounting invoice.
A simple example
A designer completes a 1,200 brand project. The invoice lists the project, the agreed amount, the issue date, the due date and payment details. When the customer pays, the seller can mark it paid or issue a receipt.