AR Grouping rules

People,

We are on 11i, and have a problem with Autoinvoice: we populate ra_interface_lines_all with some lines that has different values for field purchase_order. We want all of the lines in the same invoice, but Autoinvoice create one invoice per different value on purchase_order file.

In the documentation, we found that this field is Mandatory for the Grouping Rule standard of AR. The question is: can we setup this field for not to be mandatory?

Thanks.

Gabriel