Google translates:
"Hello. Can you help me with a concern? If I have a fixed price per night why do those who want to rent for a longer period pay less than half the price? Do I have to set something somewhere? Thanks in advance for any answers ."
@Liliana576
I checked your listing, i noticed "long term stays" (28 nights and longer) have a price of approx. € 30,- per night. Short stays have a price of € 24,- per night. So "long term stays" are more expensive !
It means you must have set a fixed price for specific months.