In order to create a not derived non-refundable rate on Booking.com log in to your Extranet. Go to Rates & Availability / Rates Plans:
Click on Add new rate plan:
Choose Non-refundable option:
In the point 5 make sure to choose Set as a new rate plan opion and click on Review:
Make sure that the rest of the settings is correct and click on Activate rate plan:
Now you should be able to map the rate in the system.