When using the Default Configuration option from the "Rebate Setup" ribbon, Sales and Purchase "No Series" will be created automatically. The purpose of this is to provide you with some default setup within your Business Central environment. 

The No Series information that is created when this is selected is as follows:

Both No Series are created using Default No's, which means Business Central will automatically number a Rebate when created, in increments of 1 from the Starting No. Manual No's is not setup here but can be changed manually within the "No Series" page if required.