Hi @p.simo90,
Thanks for that update.
If something has gone wrong with the integration, you should receive an in-app banner notifying you of any issues.
A few things I would check on your end first: ensure you have the latest version of the Klaviyo plug-in for Magento 2 (as mentioned in our documentation). Updating the extension to the most recent version may fix the problem.
Also, if you have any firewalls that you’ve set up, please ensure that the user agent Klaviyo/1.0 has full permissions. This is the user agent that all Klaviyo requests will originate from.
After you’ve ran through the above, you can try re-importing historical data through the Integrations tab (at the very bottom) that would re-sync any missing data.
Let us know how that goes for you :)