Associate Order and Product/Create OrderProduct (salesorderdetail)

Hi,

I'm trying to relate Order and Product by create Order Product (salesorderdetail) entity record using OData but I'm facing below error:

{
"error": {
"code": "-2147220970", "message": {
"lang": "en-US", "value": "The parent id is missing."
}
}
}

I also face the same error when trying from C#.

Kindly help me in associating Products to Order.

Thanks,