I need to be able to upsert line items in a NetSuite invoice with updated information from an external system.

I’ve tried to apply an internalId and externalId to the line item so I can target for update, however it doesn’t appear to be saved against the line item when GETing it back from the API.

My invoice creation payload is

{
"tranDate": "2021-07-12", 
"dueDate": "2021-07-19", 
"externalId": "sysA_INV-34698", 
"amountPaid": 0, 
"entity": {
    "id": 3127
},
"item": {
    "items": [ 
        {
            "item": { 
                "id": 374
            }, 
            "internalId": "sysA_INV-34698_JOBID-4875398"
            "quantity": 1, 
            "rate": 534.54
        }
    ]
}
}

any ideas how I can update/upsert a line item, or do I have to delete all items and re add them every time?