Overview
Our Magento 2 integration documents cover syncing a Magento sign-up form to a Klaviyo list for any future subscribers. This article covers uploading any existing subscribers to your Klaviyo list.
You can also sync customers at checkout for both email and SMS with Magento 2; however, that is not covered here.
Uploading existing newsletter subscribers for Magento 2
From your Magento store admin click on Customers > All Customers.
Filter your customers by Newsletter Subscriber and export the list as a CSV file.
From your Klaviyo account, edit and upload your CSV file to the Klaviyo list you want to sync your Magento sign-up form to.