ConvertKit (Kit) API

Create and schedule Kit newsletter broadcasts alongside social media posts with RelayAPI.

Quick Reference

Property	Value
Platform key	`convertkit`
Auth method	Kit API v4 key
Content format	HTML (plain text auto-wrapped)
Scheduling	Yes
Analytics	No

Omitting send_at schedules the broadcast about one minute ahead, using Kit's documented scheduling contract. Set send_at to an ISO 8601 timestamp for an explicit provider schedule. Although Kit can represent provider drafts with send_at: null, RelayAPI does not yet expose that remote lifecycle: null fails before provider I/O. To save a RelayAPI-local draft without creating a Kit broadcast, set the post's top-level scheduled_at to "draft".

Before You Start

You need a Kit API v4 key. Create one from the Developer tab in your Kit account settings. Kit documents that v4 keys are different from and incompatible with v3 credentials; RelayAPI validates the key with GET https://api.kit.com/v4/account and the X-Kit-Api-Key header. See Kit's API authentication guide.

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-kit-v4-api-key"
  }'

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.
`public`	boolean	No	Publish the broadcast to the Kit web feed.
`published_at`	string	No	ISO 8601 web publication timestamp.
`content_html`	string	No	Full HTML body. If omitted, plain text is auto-wrapped.
`email_template_id`	positive integer	No	Existing Kit v4 email template ID. String and zero values are rejected.
`send_at`	string	No	ISO 8601 timestamp to schedule delivery; omission schedules about one minute ahead. `null` is rejected as `PROVIDER_DRAFT_UNSUPPORTED`.

Relay media attachments are not supported for Kit broadcasts. Put images in trusted HTML referenced by content_html instead of sending a post media array.

If an older or unexpected Kit response reports a provider-side draft after a broadcast was created, RelayAPI retains the broadcast ID and terminalizes the target as failed with PROVIDER_DRAFT_REQUIRES_MANUAL_ACTION; it does not poll forever or retry the creation boundary.

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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