curl --request POST \
  --url https://api.hubapi.com/crm/objects/v3/deals/splits/batch/upsert \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "inputs": [
    {
      "id": 123,
      "splits": [
        {
          "ownerId": 123,
          "percentage": 123
        }
      ]
    }
  ]
}
'

{
  "completedAt": "2023-11-07T05:31:56Z",
  "results": [
    {
      "id": "<string>",
      "splits": [
        {
          "archived": true,
          "createdAt": "2023-11-07T05:31:56Z",
          "id": "<string>",
          "properties": {},
          "updatedAt": "2023-11-07T05:31:56Z",
          "archivedAt": "2023-11-07T05:31:56Z",
          "objectWriteTraceId": "<string>",
          "propertiesWithHistory": {},
          "url": "<string>"
        }
      ]
    }
  ],
  "startedAt": "2023-11-07T05:31:56Z",
  "links": {},
  "requestedAt": "2023-11-07T05:31:56Z"
}