Hello @CleoH,
Thanks for sharing your question with the Klaviyo Community!
I would recommend reviewing the integration guide provided by Hello Bar on how to connect with Klaviyo here: https://hellobarassist.freshdesk.com/support/solutions/articles/44001773671-how-to-sync-your-hello-bar-contacts-to-klaviyo
As part of the integration created by Hello Bar to connect and pass contacts to Klaviyo, you should be able to designate a Klaviyo list that you would want to add these subscribers to. Because contacts are being added to a Klaviyo specific list as part of this integration, you can serve these contacts automated flows by triggering your flows off of this list. This sort of flow is often times called a Welcome Series flow within Klaviyo. You can learn more about building these flows from the Creating an Email Welcome Series and Guide to Creating a List-Triggered Flow articles.
Since this connection between Hello Bar and Klaviyo is built by the developers of Hello Bar, should you need more assistance or details surrounding this integration, I would recommend reaching out to the developers at Hello Bar for further clarifications.
I hope this helps!
David