curl --request POST \
  --url https://api.example.com/v1/plus/manage/products/{id}/companies/ \
  --header 'Content-Type: application/json' \
  --data '
{
  "company": 123,
  "count": -1,
  "published": true,
  "extra": "<unknown>"
}
'

{
  "id": 123,
  "price": "<string>",
  "company": 123,
  "count": -1,
  "published": true,
  "extra": "<unknown>"
}