Invoice in FICA for charges

Hi,

My customer want to process invoice from FICA for charges - dunning charges and other charges that he post via FPE1.

Can I use the invoice process from FICA for that ?

Do I need also to create a billing document before ?

From what I understand the process is Billing doc- invoices doc and then posting the docuement.

Is it possible to collect to the invoice a document that was already being post via FPE1 without creating a billing document ?

thanks,

Vered