Hi,
If you use DIP profile, Item usage determined is SEIN and if you use Billing Form Item usage is SENI
These two are hardcoded in the Item category determination Include.
You can check VOV4, for your
Debit Memo type
+
NORM
+
SEIN
which is the item category assign
you can compare with standard IRS+NORM+SEIN = L2N
IRS+NORM+SEIN+L2N = L2S
similarly you make your settings and check
regards,
santosh