KM The only thing you can do is make sure your friend used the correct IBAN to make the transfer and the bank of your friend is not holding the payment back for some reason. You could also try to give bunq support all the payment details and let them check, but normally you should get the money immediately as soon as bunq knows about the payment.
Another thing that could've happened is that your friend accidentally made a SWIFT payment instead of SEPA. Hopefully that's not the case, but it has happened to some people before, and should be avoided if possible, as it is slow and expensive.