Issue Creating Invoice via Magento REST API: %fieldName% is not supported Error

I’m trying to create an invoice using the Magento REST API (/rest/default/V1/order/{orderId}/invoice) and I’m getting the following error:

“message”: “”%fieldName” is not supported. Correct the field name and try again.”,
“parameters”: {
“fieldName”: “AdditionalData”
}

Here’s the payload I’m sending:

{
“appendComment”: true,
“items”: [
{
“order_item_id”: 144,
“qty”: 1.000000,
“additional_data”: “{“description”:”HELLOOOOO”,”um”:”HELLOOOOO”}”
}
]
}

I also tried passing the additional_data as an extension attribute, but I received the same error. Can someone help me figure out what I’m missing?
Thanks in advance!