The integration doesn't actually work. After trying to set up the Klaviyo integration, I contacted their customer support. This is what I heard back: Looking at this profile, the information is being stored in the API event, however it hasn't been linked to any profile properties for the customer, thus it isn't in a usable format when it comes to segmentation etc.
It appears that Subbly just adds profiles to a list along with some custom properties, I would recommend to reach out the Subbly support to see if it is something they can support to link the information being passed through directly into a profile property. Please see our guide to syncing profile properties through an integration. Please also see our guide on Profile Property Action Use Cases.