Hi ,
There are lots and lots of post on this .
Please check your configuration in FBZp .
Have you define all the steps in FBZp and also make sure the Line item is due and does not have any another paymnet method in line item .
also make sure the Posting docuent date in f110 does cover the due date of your line item ,
Please check FBL1n whetehr item is due or not...