How do I register a purchase when I do not have an invoice?

You can register it by going to Cash and bank. There, you mark the account and paste the bank statement or you enter the date and amount manually via the New bank transaction button. When a matching transaction is not found, you can create a new transaction. To register the purchase, select Purchase with receipt. The amount and date are taken from the bank statement. You must then enter supplier, description, any VAT and what the purchase relates to. You can then post the transaction.

Read more in Match outgoing payments manually.