PO Approval on the basis of data provided by legacy
In my scenario, our client does not want to use the Approval of EBS, after creation of PO; Information related to PO will be send to their legacy system which has its own approval workflow, now i just have to changed the status of Purchase Order "Approve" or ''Reject" on the basis of data provided by the legacy system.
Initially, I though that there must be an API but according to you people there is no such API, so, Please advice what should I have to do.
If workflow customization (POAPPRV) is the answer; then from where i have to start.