Issue in Purchase Order Update through REST API

Summary:

Suppose one Purchase Order is having two lines, one line is in receiving and another line is in created status, so overall order is partially allocated. Customer wants to update the item for the line sequence number which is created status, But its not allowing to update through REST API.We have tried all combination in payload like, header action code = UPDATE and Detail Action Code = UPDATE. But nothing works. Please give me the solution

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