JeroenE Banks exist by the grace that people put their money in custody. That's why they have a lot of money and they can do anything with it, as long as you leave it there. In fact you have a claim on bunq , because you still have money from them. Conversely, the bank has a claim on you if you borrow or become red.
Because not all of the bank's claims to its customers have to be paid at once, the bank can spend the money that is not called up on other things, for example, they can lend it to others or invest with it. Old banks lend the money at a higher interest rate than they give in accounts, so that they can earn money with it. 1000 euros that are lent out, yields 70 euros a year, while for those 1000 euros that another customer has in the account, they only have to pay 2 euros.
Bunq chooses not to lend it, but only to invest. They must therefore keep the return on their investments higher than the interest that they must pay to their customers. Another way is to simply pay the interest from the profit they make from ordinary business operations, read; the subscription fees. That means they don't have to worry about that. If they cannot afford it, there simply arises a larger claim from the customer on bunq . However, that would undermine confidence in bunq and ensure the implosion of bunq .
For reservations on credit cards something else happens: the seller asks bunq if they want to guarantee a certain amount, the reservation. Bunq accordance with the agreement with Mastercard, Bunq is obliged to keep this money available and to release it immediately if requested. This means that bunq cannot use the money to lend or invest, because it must be immediately available for Mastercard or the seller if they so request. That money ends bunq in a suspense account at bunq and is not bunq to leave bunq . Bunq will be liable for the payment of that amount itself, or must simply be ready to pay by law.
Because they cannot make a profit on that amount and also receive no extra income for it (for example, the transaction fee that normal banks sometimes charge for credit cards), that money is nothing to do during the entire reservation. However, it must be able to be paid immediately.
If bunq were to give interest on it, that would lead to loss-making practices and that would not mean that bunq , but I, as a customer in particular, would not want that. I want bunq to be able to meet all its obligations at all times, because I am a creditor of bunq . Suppose that bunq would invest that money, then I will get involved as a creditor, because then bunq will no longer be able to pay me in full. That too would undermine confidence in bunq and could lead to an implosion.
Interest is a product from money, but then there must be a) money and b) that money must deliver something. Otherwise bunq gives bunq free money and that bunq at a given moment. Interest does not fall from the sky, it comes from other people's money, namely the debtors of bunq . In fact, we are therefore drawing interest from others (those in whom bunq invests) and bunq also has something left over in the meantime. It's just how the economy works.