API for PO receipts Update

Unit Price of multiple POs need to be changed (Increased) while Invoice has done with correct price. i have ran the API (PO_CHANGE_API1_S.update_po) to update the PO but getting the below error

Cannot update price.

Cause: You cannot update the price for one or more of the following reasons:

1. You have receipt accruals against one or more of the shipments

2. You have matched invoices to one or more of the shipments.

Please Advise on this.

Thanks,

Agam