Litestore can post each new newsletter signup to a URL you choose, for any platform it doesn't support directly.
Litestore sends each new newsletter signup from the storefront to a Klaviyo list.
Litestore sends each new newsletter signup from the storefront to a Mailchimp list.
Litestore sends each new newsletter signup from the storefront to a ConvertKit form.
The guide explains every value you set and what Litestore does with it.