The validate button will appear on the Draft page if the portal has min/max rules in place.
The validate button allows you to check that your draft is also a valid order that follows all the min/max rules before you send it out to buyers or sales reps.
If there is an issue a dialog will pop up asking if it's ok or you would like to fix it.
If you click FIX it will take you back to the working order and highlight the problem areas in red.
If the Draft is a valid order that follows the min max/rules a dialog will pop up verifying this