Oracle Cloud REST API Cancel Purchase Order

Hello,

I want to cancel a Purchase Order by REST API.

The REST API that I use is : /fscmRestApi/resources/11.13.18.05/purchaseOrders/XXXXX/action/cancel (where XXXXX is the PO_Header_Id)
Method : POST

Media Type : application/vnd.oracle.adf.action+json

User has the correct privilege to cancel the Purchase Order.

Payload : {
{
"name": "cancel",
"parameters": [
{
"cancellationReason": "Cancel a purchase order"
},
{
"initiatingParty": "buyer"
},
{
"cancelUnfulfilledDemandFlag": "false"
}
]
}

Unfortunately I get the following error : "The request content does not represent an action or it has an invalid structure."

There is a workaroud where I can cancel line by line but I want to cancel at header level.