Hey @alenjose
Great question to ask the Klaviyo Community for help with! There have been a few people who have had the same question as you. Hope I can help you start that process to solve this challenge.
When your check out is hosted on a different subdomain, it requires a custom code that allows the Klaviyo cookie to be tracked across your subdomains. @Dov responded to this same question on this community post with the custom code and where it needs to go on your site:
Please give this a thorough read through as it should fix your challenge. We are always here for you if you in the Klaviyo Community if you find yourself with more questions or challenges!