curl --request PUT \
  --url https://api.kit.com/v4/broadcasts/{id} \
  --header 'Content-Type: application/json' \
  --header 'X-Kit-Api-Key: <api-key>' \
  --data '{
  "email_template_id": 2,
  "email_address": null,
  "content": "<p>Let me introduce myself</p>",
  "description": "Intro email",
  "public": true,
  "published_at": "2023-02-17T06:43:55-05:00",
  "send_at": "2023-02-17T06:43:55-05:00",
  "thumbnail_alt": null,
  "thumbnail_url": null,
  "preview_text": "Pleased to meet you!",
  "subject": "Hello!",
  "subscriber_filter": [
    {
      "all": [
        {
          "type": "segment",
          "ids": [
            1021
          ]
        }
      ],
      "any": null,
      "none": null
    }
  ]
}'

{
  "broadcast": {
    "id": 2817,
    "publication_id": 2817,
    "created_at": "2023-02-17T11:43:55Z",
    "subject": "Hello!",
    "preview_text": "Pleased to meet you!",
    "description": "Intro email",
    "content": "<p>Let me introduce myself</p>",
    "public": true,
    "published_at": "2023-02-17T11:43:55Z",
    "send_at": "2023-02-17T11:43:55Z",
    "thumbnail_alt": null,
    "thumbnail_url": null,
    "public_url": "https://kit-greetings.kit.com/posts/hello",
    "email_address": "[email protected]",
    "email_template": {
      "id": 2,
      "name": "Classic"
    },
    "subscriber_filter": [
      {
        "all": [
          {
            "type": "segment",
            "ids": [
              1021
            ]
          }
        ]
      }
    ]
  }
}