Odoo developer - Odoo addon modification

addon created needs some modification, the following how its work
- responsible to integrate external website into odoo
- pull products from external website to odoo
- Products info is completed apart from product cost
- I need the addon to pull product cost as well

addon scenario:
- pull products from external website - done
- put it in odoo website shop - done
- customer visit odoo shop and select products to buy - done
- customer do the payment - done
- addon send the order to external website - done
- external website will check odoo wallet in thier system - done
- if wallet has enough balance the external website will send encrypted code to odoo - done
- odoo decrypt the code and send by sms to customer - done

what is missing ?

when customer buy product from odoo shop and odoo send the order to external website the purchase order not created in odoo

I need to create and approve the P.O. automatically