Nonstock Items

You should create the item from nonstock item card or from sales lines.

When a nonstock item is entered on a sales line for the first time, the program uses the information contained in the Nonstock Item table to generate an item card (look help)

What you are missing to accomplish this is on the sales order you need to select the order type as special order.

When you have done this the non stock item is a temp to select on a PO

Here it is straight from the manual

1. From the Sales & Marketing menu, click ORDER
PROCESSING→ORDERS.
2. Press F3 to create a new sales order.
3. In the Sell-to Customer Number field, enter customer number
10000.
4. Click FUNCTIONS→NONSTOCK ITEMS.
5. Select item 4100 and then click OK.
6. In the Purchasing Code field, select SPECIAL ORDER and in the
Quantity field, enter 3.
7. Release the order.
8. From the Purchase menu, click ORDER PROCESSING→ORDERS.
9. Press F3 to create a new purchase order.
10. In the Buy-from Vendor Number field, enter vendor number
40000.
11. On the purchase order line, enter item number 4100.
12. In the Quantity field, type 3.
13. In the Qty. to Receive field, type 3.