how to attach attachments using REST/SOAP API in change order

Hello Folks,

we are trying to make some changes and attach PDF files to OPEN Purchase Orders.

As we cannot attach PDF or any other attachment to Open PO, that is limited to incomplete PO. We are thinking to use change orders.

For that, we are using changePurchaseOrder Operation of PurchaseOrderServiceV2 SOAP API but using that we are able to make changes in fields but cannot attach files to Change order. hence, can't attach files to OPEN POs.

WSDL used : https://xxx.oraclecloud.com/fscmService/PurchaseOrderServiceV2?WSDL

Could you please suggest a way to attach PDF files to OPEN POs using Change Order?