While Klaviyo does not have a built-in integration with Justuno, you can still integrate your Justuno account with Klaviyo. This is possible via an integration available through Justuno.
Before you get started, you must already have existing lists in your Klaviyo account that you are hoping to connect to Justuno.
Add the Justuno Integration
Once you've generated a private API key, you can copy it and paste it into Justuno.
Log into your Justuno account, click Promotions, and select Edit Integrations from the Edit dropdown of the Promotion you'd like to integrate.
Find Klaviyo from the available list of integrations. Click Connect and enter your API key along with the List ID of the Klaviyo list you would like to connect.
Click Save and Close to complete the integrations.
Your Justuno account will now sync new signups to your Klaviyo list as they come in.
You can also view integration instructions on Justuno's website
Data Synced to Klaviyo
From Justuno, Klaviyo pulls in your subscribers to the list you've specified in Justuno.