Find payment order referenced invoices through SDK

Hello,

Upon OnSave-Validation event of payment order, I need to read the list of the supplier invoices referenced to the just added Payment order in order to create some validation tests.

It seems that the object does not have link to the invoices payed in this payment order.

this.BusinessDocumentFlow.Count() returns no entries.

Can someone point me how can i get the list of the supplier invoices linked to the payment order ?

Thanks, Tamir