Vendor User Defined Validation is selected when setting up the Purchase Order Setup. If you select user defined fields and elect to use a list to validate them when entering purchase orders, you will need to set up the Vendor User Defined Validations.
PUR > Purchasing Special Functions > Vendor Defined Validation Setup
When you check the "validate" check box next to a vendor flex field in vendor flex field set up, whatever that flex field is will become an option in user-defined fields. That defined field will need to have its options applied to it, the code and description that makes up those options. Once set up and a vendor are entered the flex field you created will have a drop down box and require a selection from the list of options you created.
User Defined Field – the flex field name
Code – each code represents an option for the flex field pull down menu
Description – the long description of the code