The online accounting program mKsiegowa.pl, you can:
- Invoice based on pre-prepared Delivery
- Invoice based on several Delviery documents
On the sale use Invoice option for GM.
After selecting the Direct Document click 
on the right to issue an invoice.
Here you can submit the final invoice to the Delivery when Delivery could be prepped against the pro-forma invoice paid in advance.
Note: If there is no icon in the row specified document PZ This means that the invoice for this document has been issued.