Klaviyo

To authenticate with Klaviyo you'll need to attain a private and public API key. Please refer to Klaviyo's website on where these can be attained.

Get API credentials | Klaviyo DevelopersAPI Reference & Technical Guides | Klaviyo Developers

Once you have you credentials in hand you'll want to add a new Klaviyo app connection and enter your credentials in the Edit Connection Details page.