how cancel a Internal Requisition in PO?

We have an AP/AR invoices between US and UK created for an Internal Requisition in Purchasing, now users want to reverse all processes from accounting invoices to Inventory items in the Purchasing.

We have:

AP Invoice : 47866-83 Status: PAID (300511)

AR Invoice: 47866 - Status COMPLETED- Receipt applied (WIRE-05/17/16-464886

OM SO: 10903430 Status: CLOSED

PO Requisition: 108366. Status: APPROVED

We're considering cancel AP/AR manually but How can we cancel/reverse the PO Requisition?

If it status is APPROVED, how can we cancel it? Will it create a transaction in OM? or should we create a manual RMA in OM to reverse that step?