When creating a new Lead Capture form you can choose to send submissions directly to your ConvertKit account.
Step 1 - Add A New Provider
Under the integrations tab select 'providers' and click the 'add a new provider button'
Step 2 - Connect To ConvertKit
To connect to ConvertKit you will need your API Key and your API Secret. You can obtain these from ConvertKit here.
Enter these details in the form as shown below:
Step 3 - Select A Tag
When someone opts-in to your form, a ConvertKit tag will be applied to their record.