curl --request DELETE \
  --url https://api.upwell.com/api/rest/invoices/{invoiceId}/documents/{id} \
  --header 'Content-Type: application/json' \
  --data '
{
  "id": "<string>",
  "invoiceId": "<string>"
}
'

{
  "deleteFileAssociations": {
    "affectedRows": 123,
    "returning": [
      {
        "associationId": "<string>",
        "fileId": "<string>",
        "id": "<string>"
      }
    ]
  }
}