ConvertKit (Kit) API

Create newsletter broadcasts via ConvertKit using RelayAPI — draft email campaigns alongside social media posts.

Quick Reference

Property	Value
Platform key	`convertkit`
Auth method	API Key + Secret
Content format	HTML (plain text auto-wrapped)
Scheduling	Yes
Analytics	No

By default, broadcasts are sent immediately when published. Set send_at in target_options to schedule for a specific time, or omit it for instant delivery.

Before You Start

You need a ConvertKit API key and API secret. Get these from your ConvertKit account settings.

Connect

curl -X POST https://api.relayapi.dev/v1/connect/convertkit \
  -H "Authorization: Bearer $RELAY_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "api_key": "your-convertkit-api-key",
    "api_secret": "your-convertkit-api-secret"
  }'

Send a Broadcast

curl -X POST https://api.relayapi.dev/v1/posts \
  -H "Authorization: Bearer $RELAY_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "Our latest newsletter content...",
    "targets": ["acc_convertkit123"],
    "scheduled_at": "now",
    "target_options": {
      "convertkit": {
        "subject": "Weekly Newsletter #10",
        "preview_text": "What we shipped this week"
      }
    }
  }'

`target_options` Fields

Field	Type	Required	Description
`subject`	string	No	Email subject line. Falls back to first line of content.
`preview_text`	string	No	Description/preview text.
`content_html`	string	No	Full HTML body. If omitted, plain text is auto-wrapped.
`send_at`	string	No	ISO 8601 timestamp to schedule delivery. If omitted, sends immediately.

Automations

Kit (formerly ConvertKit) uses the v4 API under https://api.kit.com/v4. Triggers fire on subscribe lifecycle and tag events.

Triggers

Type	Fires on
`kit_subscriber_activate`	Subscriber becomes active
`kit_form_subscribe`	Form submission
`kit_tag_add`	Tag applied to a subscriber

Send nodes

Node	Endpoint	Required fields
`kit_add_subscriber`	`POST /subscribers`	`email`, optional `first_name`
`kit_add_tag`	`POST /tags/{tag_id}/subscribers`	`tag_id`, `email`
`kit_send_broadcast`	`POST /broadcasts/{id}/send`	`broadcast_id`

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ConvertKit (Kit) API

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