Outside Processing Purchase Approvals

I set up n item routing with outside processing, and set the P4310 version processing options to use BP approval route code and set up the 'OO' processing options, but it would not create the PO.  I changed that processing option to USERID, set up the 'OO' and specified the approval route code in the user's profile, but it still wouldn't create the PO.  It will only create the PO when I change the P4310 processing option to blank.  How do you get PO approvals to work with outside processing?