3557846 - All Partner functions maintained in the BP are not getting populated in the partner data tab in purchase order

When creating a PO with reference PR, or create PO in Create Purchase Order - Advanced(ME21N), these Partners are missing.

• Although Partner Roles (PI, OA etc.) have been maintained in the Maintain Business Partner(vendor master), these same Partner Roles cannot be copied to PO when creating the PO with reference PR.
• Adding these Partners to the created PO afterwards and saving does not work either, these are blanked / reset.

SAP S/4HANA Cloud Public Edition

*Note - In BP, the partners (VN, OA, PI etc.) have already been maintained correctly.*

Missing additional customizing for Partner Schemas.

1. Use SSCUI 103122 Assign Partner Schemas to Document Types to find out the relevant Partner Schemas by document type. 
2. Then, use SSCUI 102524 Define Partner Schemas in Purchasing Documents, select the Partner Schemas (from step 1), and set the flag 'Search at Higher Level' for relevant partner function (PI, OA, etc.). 
3. Save the configuration.

SAP Note 459350 - FAQ: Partner determination in purchasing

SAP Note 550844 - FAQ: MRP areas

Partner function, VN, OA, PI, GS, purchase order, purchase requisition, business partner , KBA , MM-PUR-GF-PA-2CL , Partner (Public Cloud) , Problem