Munkhdelger Bunq accounts can only receive payments in the same currency. For example, an Euro sub-account can only receive Euros, a Dollar sub-account can only receive Dollars. Unfortunately, bunq doesn't support QAR sub-accounts.
Payments sent in a different currency can't be received and are sent back to the sender.
You have to ask the vendor to send the refund in Euro's (or any other currency, as long as you have a sub-account in this currency).