Questions about Integrating with Klaviyo
Last updated on October 21, 2026
I successfully integrated my Klaviyo account to the Vitals app. However, the emails captured are not being added to my selected Klaviyo list. What's wrong?
This might be caused by Klaviyo's Double Opt-in feature, enabled by default after creating a Klaviyo list.
How this feature works is that when an email address is captured on Shopify and is detected by Klaviyo, it will send an initial message to the email address first, asking the recipient to confirm the subscription.
Once the recipient receives and agrees to that opt-in email, that is the time that the email address will be successfully subscribed to the selected Klaviyo list.
To know more about this feature and how to disable/enable it, you can read more on Klaviyo's Help Center here: Guide to The Double Opt-In Process.
Do I need a Klaviyo API key?
No. Go to Integrations > Connect Klaviyo and approve Vitals in Klaviyo; no key is needed (see Connect Klaviyo to Vitals in three steps). Stores connected with a key earlier keep syncing.
Can the Back In Stock App be connected to my Klaviyo account?
Yes. Back in Stock, Product Reviews, Wishlist, Upsell Builder, Pop-ups and Order Tracker can send events to Klaviyo, so you can start flows from them. See Send Vitals events to Klaviyo.
Will sending Vitals events to Klaviyo change my existing flows?
No. Vitals does not create, copy or edit your Klaviyo flows. Your flows, lists and list sync continue working as before. Vitals events are new metrics, and nothing happens unless you build a flow using them.
How can I avoid duplicate emails when I create a Klaviyo flow?
Product Reviews and Back in Stock can already send emails for some of the same moments. Before creating a Klaviyo flow, choose one sender: keep the Vitals email, or turn it off in the app and let Klaviyo send it. The Back in Stock restock alert is always sent by Vitals and cannot be turned off, so do not create a Klaviyo flow that sends the same restock alert.