Kit Integration

3 min readUpdated June 21, 2026

Kit (formerly ConvertKit) is an email marketing platform built for creators. WP Smart Consent integrates with Kit via the API v4, subscribing opted-in contacts to one or more Kit forms in real time.

Enabling the Integration#

In the WP Smart Consent dashboard, go to CRMs & ESPs, find the Kit card, open the Connection tab, and paste in your API key. Toggle the integration on and save. WP Smart Consent connects to your Kit account and populates the form picker with your available forms.

To find your API key, log into Kit and go to Settings → Developer → API Keys. Copy the public API key — Kit v4 uses X-Kit-Api-Key header authentication.

Custom Fields#

Kit supports custom subscriber fields defined in your Kit account under Subscribers → Custom Fields. In the Custom fields tab, add a row, select the WPSC source field on the left, and enter the Kit custom field name on the right — exactly as it appears in your Kit account. These are sent inside the fields object in the API payload.

Standard Kit fields (first_name, last_name) are always sent automatically and do not need to be mapped in the Custom fields tab.

Field Mapping#

The Field mapping tab maps WPSC fields to Kit subscriber field names. Kit’s subscriber model accepts email_address as the top-level identifier, with first_name and last_name as standard fields and all other data sent inside a fields object using your Kit custom field names as keys.

How It Works#

Kit’s model uses forms rather than lists — a subscriber is added to the Kit system by being subscribed to a specific form, which can then trigger sequences, tags, and automations inside Kit. WP Smart Consent sends a POST to https://api.kit.com/v4/forms/{form_id}/subscribers for each selected form. If multiple forms are selected, one call is made per form.

The payload structure is:

json

{
  "email_address": "jane@example.com",
  "fields": {
    "first_name": "Jane",
    "last_name": "Smith"
  },
  "tags": ["12345"]
}

Forms Tab#

The Forms tab is where you select which Kit forms opted-in contacts are subscribed to. The list is populated automatically from your Kit account after the API key is saved. Select one or more forms — each triggers its own subscriber call.

Options#

The Options tab has three settings.

Update existing contacts — controls whether an existing Kit subscriber matched by email is updated on each opt-in.

Send on unchecked — when enabled, contacts are forwarded to Kit even when the opt-in checkbox was not ticked.

Tags — a comma-separated list of Kit tag IDs to apply to every subscriber. Tag IDs are numeric and can be found in Kit → Subscribers → Tags. Tags are passed as an array of string IDs in the API payload.

Screenshot of the “Options” tab in Kit Creator CRM settings. “Update existing contacts” is toggled on. “Send on unchecked” is off. There is a field for comma-separated tags, an active “Save Kit” button, and the kit status is shown as inactive.

Troubleshooting#

Form list not populating — confirm the API key is correct and saved. The form list is fetched from GET /v4/forms after save. A wrong key returns a 401 and the list stays empty.

Subscriber not appearing in Kit — confirm at least one form is selected in the Forms tab. Kit requires a form to be specified — there is no global subscriber list. Check the WPSC Logs tab to confirm the opt-in event fired.

Custom field values not saving — confirm the destination key exactly matches the custom field name in Kit. Custom field names are case-sensitive and must already exist in your Kit account before values can be written to them.