Convert requisitions to PO's

Migrated from GP2010 to GP2015R2 and migrated from BP to workflow 2.0

I have a purchasing department that handles all the PO creation after the requisition is complete. I can't find how to give them access to generate the PO from the requisition.

I have created a list view that shows all requisitions but they don't have the purchase button. (Still not sure at 100% that everything shows in the list) and if they go in the purchase requisition inquiry, the button purchase is there but GP tells me that the user doesn't have the security to open the window

What security do they need to be able to generate the PO's ?

Thanks