In the Pricing section not supported fields are indicated: Price per person, Price for children's extra bed, Price for additional adult bed.
At the moment, Booking.com does not support the Extra bed fields by default. Therefore, the price for additional space is not synchronized. If you see this error, first of all you need to remove the prices for additional beds or disable synchronization with Booking.com. If you are going to disable synchronization with Booking.com, please consult MaxiBooking technical support to avoid overbooking or shutting down your hotel on Booking.com side.
To include additional seats, you must make a request to Booking.com to add this option to your hotel. After this field appears in your hotel profile on Booking.com, you can add prices for additional beds or resume the synchronization if it had been disabled.