When implementing an XML interface, there is a setting that a property can choose to 'automatically assign a room' to an online booking or not. This choice can have ramification to an XML developer, so read the article on this choice at: https://support.bookingcenter.com/index.php?/Knowledgebase/Article/View/369 to better lead your customer to a wise decision.

If you are developing an XML solution for an Owner(s) of Unit(s) part of an Owner Channel Program (https://www.bookingcenter.com/nontraditional/), then the ability to make changes to the 'Auto Assign Room' is not within your command - that setting affects all bookings within the PMS and thus is the choice of the owner of the PMS.  BookingCenter won't be able to assist when attempting to Save a Booking and receiving this message, as the message displays that a specififc room is not available for all days the booking is attempting to be saved.  In such error conditions, the XML developer should provide error reporting to their Unit Owner(s) to make sure the booking is saved manually via the PMS, Owners Area, or Agents Area.