You can find the setting to Enable or Disable the Ready to Post functionality for either Invoices or Requisitions by following the steps below.
Click the Red 21 at the left of the tool bar
Select Setup and Company Setup (as seen below)
Select the Invoices/STmts/Acct Reg tab (as seen below)
Select or Deselect the appropriate tab for either Invoice or Requisition (as seen below)
If you want to find out how to make sure your techs mark their invoices as Ready to Post, please follow the instructions here.