@Veerle15
Check if the guest created the account very recent (being a new member without first review)
Bu sure also ID is verified (or ask guest to do this)
Ask the guest some questions, like "what is the purpose of your stay in Gent "?
You offer 50% monthly discount on such stays + extra 20% promotional discount for first 3 bookings
BTW
I would not recommend for a new host to start with a "long term stay" reservation (28 nights and longer). Such reservations have special terms and rules, check HELP files.
There is also a community for The Netherlands and Belgium (Dutch language).