curl --request POST \
  --url https://api.example.com/concat/save \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "languageId": 1,
  "categoryId": 123,
  "postDate": null
}
'

{
  "success": true,
  "data": "<unknown>"
}