RE: Adding Item Attribute FactBox part page to Purchase Order Line page
You have to add the fact box to the Purchase order page and not to the sub page showing the line.
And to let the fact box know where it should get it's data from you need to add:
Provider = PurchaseLines; (Or the correct naming of your line variable).
That connects the factbox in the head to the records on your sub page.
This is how it is done in the standard Page 50 for Purchase orders:
part(Control3; "Purchase Line FactBox")
{
ApplicationArea = Suite;
Provider = PurchLines;
SubPageLink = "Document Type" = FIELD("Document Type"),
"Document No." = FIELD("Document No."),
"Line No." = FIELD("Line No.");
}