curl --request POST \
  --url https://api.paubox.net/v1/orca/{username}/subscribers_bulk_create \
  --header 'Content-Type: application/json' \
  --header 'authorization: <api-key>' \
  --data '
{
  "subscribers": [
    {
      "email": "jsmith@example.com",
      "first_name": "<string>",
      "last_name": "<string>",
      "custom_fields": [
        {}
      ]
    }
  ],
  "subscription_list_id": "<string>"
}
'

{
  "data": {
    "num_subscribers_added": 123
  }
}