Hi ,
check if any type of clearing lock or restriction i.e "8" is there in debit items .if non is there
if your clearing is only based on documentnumber then the below clearing variant with two steps will work for both cash and check
STEP 1--- Grouping string
char-018 (document number)
STEP 2--- grouping string sorting string
char-018 (document number ) sort character -010 (due date)