Hi,
In the configuration path for Utilities->Invoicing->
Invoice Processing->->Item selection in Account Maintenance/Define Sub-Items
For Clearing Types R4, R41, R42, and R43:
Specify Main Transaction 0080 (and Sub Transaction if necessary), you need to select "9" in the "OIsel" column (Open Item Selection).
This should accomplish what you want.
I hope this helps.
Regards,
Ivor Martin