curl --request POST \
  --url 'https://api.onesignal.com/notifications?c=email' \
  --header 'Authorization: <authorization>' \
  --header 'Content-Type: application/json' \
  --data '{
  "app_id": "YOUR_APP_ID",
  "include_aliases": {
    "external_id": [
      "<string>"
    ],
    "onesignal_id": [
      "<string>"
    ]
  },
  "target_channel": "email",
  "include_subscription_ids": [
    "<string>"
  ],
  "email_to": [
    "<string>"
  ],
  "included_segments": [
    "<string>"
  ],
  "excluded_segments": [
    "<string>"
  ],
  "filters": [
    {
      "field": "first_session",
      "key": "<string>",
      "relation": ">",
      "value": "1"
    }
  ],
  "email_subject": "This is your email subject.",
  "email_preheader": "<string>",
  "email_body": "<string>",
  "name": "<string>",
  "template_id": "<string>",
  "custom_data": {},
  "email_from_name": "Your Company",
  "email_from_address": "<string>",
  "email_sender_domain": "<string>",
  "email_reply_to_address": "<string>",
  "include_unsubscribed": true,
  "disable_email_click_tracking": true,
  "send_after": "<string>",
  "delayed_option": "<string>",
  "delivery_time_of_day": "<string>",
  "idempotency_key": "<string>"
}'

{
  "id": "<string>",
  "external_id": "<string>",
  "errors": {
    "invalid_email_tokens": [
      "<string>"
    ],
    "invalid_aliases": {
      "external_id": [
        "[\"user_id_1\", \"user_id_1\", \"user_id_2\"]"
      ],
      "onesignal_id": [
        "[\"1589641e-bed1-4325-bce4-d2234e578884\", \"1589641e-bed1-4325-bce4-d2234e578884\", \"1589641e-bed1-4325-bce4-d2234e578884\"]"
      ]
    },
    "invalid_player_ids": [
      "<string>"
    ]
  }
}