curl --request POST \
  --url https://api.shoppex.io/dev/v1/products/{id}/variants/{variantId}/serials \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "serials": "ABC-123\nXYZ-789",
  "remove_duplicates": true
}
'

{
  "data": {
    "added_count": 2
  }
}