curl --request POST \
  --url https://api.upwell.com/api/rest/invoices/{invoiceId}/documents \
  --header 'Content-Type: application/json' \
  --data '
{
  "input": {
    "base64": "<string>",
    "filename": "<string>",
    "mimeType": "<string>",
    "sourceSystem": "<string>",
    "sourceSystemId": "<string>",
    "type": "<string>",
    "visibleToCarrier": true,
    "visibleToCustomer": true
  },
  "invoiceId": "<string>"
}
'

{
  "createInvoiceDocument": {
    "documentId": "<string>",
    "id": "<string>"
  }
}