By means of a personal example, here's why we need this feature: proof of payment for single transactions.
An amount has been debited from my account. The supplier has blocked my access to their service and insists that they cannot see the payment on their side. I cannot send the supplier anything that uniquely confirms that the payment was actually received by them (if Bunq is to be believed that a debit of my account corresponds to a receipt on the supplier side). It seems as if my money has disappeared into the Ether. Is it possible that Bunq cannot confirm the end-to-end completion of the transaction and therefore cannot provide the functionality for "Proof of Payment"?