Send Popup Subscribers to Klaviyo from Shopify

To send popup subscribers to Klaviyo, connect your popup app to Klaviyo with a private API key, choose the list each popup feeds, and build a welcome flow that starts when someone joins that list. After that, every sign-up from your email popup, including an exit intent popup, lands in Klaviyo on its own. No weekly CSV exports, no subscribers who wait days for their welcome code.

This guide walks through the setup with Sam FOMO, explains the opt-in choice that trips up most stores, and shows how to check that every subscriber arrived. If you haven’t built the popup yet, start with our email popup guide for Shopify.

Why send popup subscribers to Klaviyo instead of exporting a CSV?

A direct sync gets the welcome email out while the shopper still remembers your store. With a CSV, someone has to export, clean and import the file, and every subscriber in between waits.

A CSV still has a place. It works as a backup and for tools with no direct connection. But if Klaviyo sends your welcome emails, a sync is the simpler setup.

What do you need before you connect Klaviyo?

You need three things ready:

1. A Klaviyo account where you can create API keys.
2. A list for popup sign-ups. Create it in Klaviyo first. One list per offer, such as “Popup: 10% welcome”, makes reporting easier.
3. A working email popup with your offer and trigger already set. Our email popup user guide shows each screen.

Decide one more thing up front: single or double opt-in for that list. It changes when people appear in Klaviyo, so it gets its own section below.

How do you connect a Shopify popup to Klaviyo with Sam FOMO?

Sam FOMO is our sales popup and social proof app. It is free to install and rated 4.6★ from 17 reviews on the Shopify App Store (Oct 2026). The Klaviyo connection lives inside each email popup.

Step 1: Open the Customer Data card

Open Popups, edit your email popup, and go to the Triggers & Placement tab. Scroll to the Customer Data card. You’ll see two options: Sync to Shopify Customers and Klaviyo.

Step 2: Create a private API key in Klaviyo

Click Connect Klaviyo. The window lists three steps:

1. In Klaviyo, go to Settings → Account → API keys. The window has a direct link.
2. Click Create Private API Key, name it “Sam FOMO”, choose Custom Key and set Accounts: Read, Lists: Full, Profiles: Full and Subscriptions: Full.
3. Create the key, copy it and paste it into the Private API key field.

Copy the key right away. Klaviyo says you “cannot view your private API keys in Klaviyo” after creating them, and you “cannot edit a private API key after it’s been created” (Klaviyo Developers). If you miss a scope, delete the key and create a new one. The app stores the key encrypted and only uses it to send subscribers to Klaviyo.

Step 3: Choose the list

Once the key is accepted, the card shows Connected and your account name. Tick Send subscribers to Klaviyo and choose a list under Klaviyo list. If you just made the list, click Refresh. The popup won’t save with the box ticked and no list chosen.

Step 4: Decide on Shopify Customers

Sync to Shopify Customers is a separate checkbox. It creates or updates a customer in Shopify Admin, tagged sale-boost and subscribed to email marketing. Keep it on if you want popup sign-ups in your Shopify customer list too. Turn it off if Klaviyo is the only place you need them.

Step 5: Save and choose what happens to past sign-ups

Click Save. If the popup already has subscribers and you just turned Klaviyo on, the app asks Send existing subscribers to Klaviyo? Choose Send to add them to the list with their original sign-up date, or Only new subscribers to start fresh.

Should the Klaviyo list use single or double opt-in?

Pick based on what you want more: a fast welcome or a confirmed list. Klaviyo explains that on a double opt-in list, “everyone who subscribes to that list must confirm their interest before they’re added,” while with single opt-in “subscribers do not need this additional confirmation” (Klaviyo Help Center).

Sam FOMO shows which one you picked. Under the list, it says “Single opt-in list. Subscribers join right away,” or shows a note that Klaviyo emails a confirmation link first. That note links to the list’s settings in Klaviyo if you want to switch.

One thing to watch: the popup shows the discount code on the thank-you screen right away, whatever the list setting. With double opt-in, people who never confirm still saw the code but won’t get your emails. That’s fine. Just don’t write “check your inbox for your code” if the code is already on screen.

What data reaches Klaviyo with each subscriber?

Each subscriber joins the list you chose. The popup name and the coupon code are saved on their Klaviyo profile. Name, phone and country go along too if your popup form collects them.

The popup name is the useful part. It tells you which popup, and so which trigger and offer, brought each person in. Open one test profile in Klaviyo to see the exact property names before you build filters on them.

Klaviyo flows let you “use profile filters, including Properties about someone, to narrow who qualifies after a flow is triggered” (Klaviyo Help Center). So one welcome flow can send different copy to people who came from the exit intent popup and people who came from the scroll popup.

How do you set up an exit intent popup that feeds a Klaviyo welcome flow?

The trigger and the Klaviyo connection are independent. Set the trigger, connect the list, and build the flow in Klaviyo.

1. Set the trigger. On Triggers & Placement, set Trigger condition to On exit intent (desktop only). Our exit intent popup examples cover offers that suit a visitor who is leaving.
2. Cover mobile with a second popup. Exit intent doesn’t fire on phones. Create a second popup for mobile with After delay or On scroll, and send it to the same list. See exit intent popups on mobile for the options.
3. Name each popup clearly, such as “Exit intent desktop, 10% off”. The name travels to Klaviyo, so a clear name makes filters easy.
4. Build a list-triggered flow. Klaviyo’s welcome series “triggers when new subscribers are added to a list” (Klaviyo Help Center). Put the welcome code in the first email, so people who closed the thank-you screen still have it.
5. Space the follow-ups. Klaviyo suggests a “24 hour (or longer) delay” between the first and second email of a welcome series (same source).

If you’re still choosing the offer, our post on email popup discount offers compares the options and the limits to set in Shopify.

How do you check that the sync is working?

Test once with a real sign-up, then check the status in the app.

• Sign up in a private window. For an exit intent popup, browse for a moment on desktop, then move the cursor up past the tabs. Use an address you can open.
• Open Popups > Subscribers. The Synced to column shows a badge per destination: a green Klaviyo badge when the subscriber is in, Pending while waiting to send, or Klaviyo failed. Hover a failed badge to see the error.
• Filter by Sync status. Choose Failed, Pending or Synced to find problem rows fast.
• Fix, then resync. After you fix the cause, click Resync failed to send those subscribers again.
• Check Klaviyo. Find the test profile and confirm it’s on the list. On a double opt-in list, confirm the email first.

If the API key stops working, for example because someone deleted it in Klaviyo, the app shows a banner: “Update your Klaviyo API key to keep sending subscribers. New subscribers are saved and will be sent after you update it.” Create a new key with the same four scopes and paste it in through Update API key.

What mistakes break a popup to Klaviyo sync?

• Missing a scope on the key. All four are needed. Klaviyo keys can’t be edited, so create a new one.
• Expecting double opt-in sign-ups to appear at once. They join only after they confirm.
• Sending every popup to one list. You lose the easy split between offers. Use the popup name or separate lists.
• Two welcome flows for one person. If popup sign-ups reach Klaviyo by more than one path, check which flows they enter so nobody gets two welcome emails.
• No welcome email at launch. Build the flow before the popup goes live.
• Fake urgency in the popup. A “code expires in 5 minutes” timer on a code that never expires misleads shoppers. Our social proof guide covers honest urgency and real signals.

Once the sync runs, the popup does one job: collect consent with a clear offer. Klaviyo does the rest. The full popup setup, from offer to Klaviyo, is in the Sam FOMO email popup guide.