Automatic invoice in the back ground

Hi,

I have seen a BAPI to create invoice and it is working fine for me.

BAPI_BILLINGDOC_CREATEMULTIPLE

The client requirement is they do not want to create Invoice manually,they want to do it automatically.They will only do PGI for deliveries.Once PGi is done ,Invoice needs to created in back ground.

Is there any back ground job available to create Invoice.