Fix some issues php

Hi
I need to fix some issue i see in this php stock managment (below)
https://www.sourcecodester.com/sites/default/files/download/oretnom23/sms.zip

Is has issue in
1- error in creat a new sale
2- cant edit the cost at new po
3- when i recived some items will be not keep pending items in back order (error)
4- need small script to import csv for all thing

Please tell your price in first line
And check all to be sure all work fine