Creating invoice in Zoho inventory, success but salesorder_id is empty

Creating invoice in Zoho inventory, success but salesorder_id is empty

Hello,

I'm sending a request go the API with such json data: 
{"date":"2016-12-19",
"salesorder_id":"495465000000101015",
"customer_id":"495465000000083222",
"line_items: [{"item_id":"495465000000076001","rate":6,"quantity":1}]
}
The invoice is created but, there is no order id attached to it. I can't see linked salesorder in Invoices view. The response I receive:


stdClass Object
(
    [code] => 0
    [message] => The invoice has been created.
    [invoice] => stdClass Object
        (
            [invoice_id] => 495465000000102041
            [documents] => Array
                (
                )

            [invoice_number] => INV-000022
            [salesorder_id] => 
            [salesorder_number] => 
            [date] => 2016-12-19
.
.
.