curl --request POST \
  --url https://api.apexxcloud.com/api/v1/files/multipart/{uploadId}/upload \
  --header 'X-Access-Key: <api-key>' \
  --header 'X-Signature: <api-key>' \
  --header 'X-Timestamp: <api-key>'

{
  "data": {
    "partNumber": 123,
    "ETag": "<string>"
  }
}