Thank you.
In standard delivered customizing the item category DLX has FKREL blank.
Are you sure your business neds to have it relevant for billing, with FKREL = 'A' ?
If you decide to change FKREL of DLX in transaction VOV7, please run report ZLFFKREL in note 319866 to update LIPS-FKREL of that delivery.
Then run RVDELSTA to update its VBUP record.
Afterwards the delivery will not be relevant for billing anymore.
If you prefer to keep FKREL = 'A' for DLX, but you want make the delivery not billeable, then you could clear its LIPS-FKREL (by SE16), then run RVDELSTA
Best regards,
Ivano.