The BIC is PESOBEB1. This is the identification code for PREPAYMENT SOLUTIONS EU S.A., the licensor for Monese in the European Economic Area.
Your IBAN starts with "BE*" and has only 16 digits, in contrast to a German IBAN which starts with "DE*" and has 22 digits.
You can find the bank code when you click on "Details" in your Monese app in the account on the home page, directly under your account balance.