When a nonstock item is on a Purchase Order it is not actually received since it doesnt create an inventory receipt.  In that case the the quantity field will be inaccessible and the notice that it is nonstock will be displayed

This line can be ignored and the PO can then be closed like normal.

Payable For Nonstock Items

When entering payables for Nonstock items, the user will have the ability to track the expense to the specific GL.  This is handled when entering the payable and more can be found in the Accounts Payable documentation.