HI,
in billing rebates first of all you have to do the baseline customization.
Maintain Agreement types.*
Maintain Condition type groups.*
you also need to create a new table for matkl and the rest of your keys - before do this check if there is any condition rebate table which fullfils your criteria.
after that add this new table to your access sequense. I assume that you already have a rebate condition and access sequence.
finally assign condition type\tables to your condition type group and also assign agreement types to condition type group*
* note that you donot need to do these steps if you already have this configured to your system.
Hope it helps.
Regards