Is it not possible to transfer PO Header DFF to AP Invoice header

Is it not possible to transfer PO Header DFF  to  AP Invoice header ?

Single invoice can be matched to multiple PO's and in such a case the question will be to which PO header DFF must be copied. 

Currently there is no such functionality available.

However it is possible to transfer the purchase order PO distribution DFF. There is a setup option of "Transfer PO Distribution Additional Information" in "Manage Invoice Options" (in the section matching). When you enable that option, DFF information from PO distribution will get copied to AP Invoice Distributions. 

 Also the DFF's must be setup and deployed for both Purchase Order Distributions and Payables Distributions for the same attributes.

Setup and Maintenance
Select your Implementation Project
Go to Manage Descriptive Flexfields

Search and pull up for Payables Application and then Purchasing Applications - make sure the definitions are the same.

SQL's to check

select * from FND_DF_FLEXFIELDS_B where descriptive_flexfield_codein
('AP_INVOICES','AP_INVOICE_DISTRIBUTIONS','PO_DISTRIBUTIONS')

select * from FND_DF_SEGMENTS_b where descriptive_flexfield_code in
('AP_INVOICES','AP_INVOICE_DISTRIBUTIONS','PO_DISTRIBUTIONS')

Run

select
po.segment1, pod.*
from po_headers_all po ,po_distributions_all pod
where po.PO_HEADER_ID = pod.PO_HEADER_ID and
pod.attribute1 is NOT NULL and pod.CREATION_DATE > '20-JAN-2016'

select
ap.invoice_num,
apd.* from ap_invoices_all ap,
ap_invoice_distributions_all apd where
ap.Invoice_id = apd.invoice_id and apd.po_distribution_id in (Select po_distribution_id from po_distributions_all pod where pod.attribute1 is NOT NULL and pod.CREATION_DATE > '20-JAN-2016')