Best practice for communication between AP and PO requestor

Summary:

When a PO fails to match perfectly to an invoice, the AP team will need to connect with the PO requestor for clarification. This is done outside of Oracle using email. We are looking for a more efficient way of communicating with the PO requestor:
-Log communication in Oracle for future audit trail in case anything needs to be adjusted
-Efficiently keep communication in one system
-Allow AP to easily ask PO requestor for information without having to look up contact info in several screens

What are best practices for larger organizations with many sites and requestors?

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