How to send Confirmation Emails with Klaviyo When Customers Sign Up for Back‑in‑Stock Alerts

STOQ automatically sends a signup metric to Klaviyo every time a customer registers for a back-in-stock alert on your store. You can use this metric to trigger a Klaviyo flow that sends a confirmation email, a thank-you message, or a product recommendation — all without any manual work. This guide walks you through creating a Klaviyo flow that fires as soon as a customer signs up.

Before You Begin

Make sure you have the following before you create your confirmation flow:

• STOQ installed and active on your Shopify store
• A Klaviyo account connected to STOQ (either through the Sync to Klaviyo integration or by selecting Klaviyo as your email provider for back-in-stock notifications)
• At least one customer signup so the metric appears in your Klaviyo account

Tip: The signup metric is sent to Klaviyo automatically as soon as customers register for alerts. You do not need to enable a separate setting for it — it works as long as your Klaviyo connection is active.

How the Signup Metric Works

STOQ sends a metric to Klaviyo each time a customer signs up for a back-in-stock alert. This is the metric you will use as the trigger for your confirmation email flow.

• OAuth connection (recommended): The metric is named Customer signed up for alert (STOQ).
• API key connection (legacy): The metric is named Stoq - Customer signed up for alert.

The metric includes detailed event properties about the customer, the product they signed up for, and your store. You can use these properties as template variables in your confirmation email.

Event Properties Sent with the Metric

The table below lists every property STOQ sends with the signup metric. Use these as dynamic variables in your Klaviyo email template.

How to Create a Confirmation Email Flow in Klaviyo

Follow these steps to build a flow that sends a confirmation email when a customer signs up for a back-in-stock alert.

Step 1: Create a New Flow

1. Log in to your Klaviyo dashboard.
2. Click Flows in the left sidebar.
3. Click Create Flow.
4. Select Build Your Own (do not use a pre-built template).
5. Give your flow a descriptive name, such as "Back-in-Stock Signup Confirmation."
6. Click Create Flow.

Step 2: Set the Trigger to the STOQ Signup Metric

1. In the flow editor, click Select a trigger in the trigger block.
2. In the right sidebar, find Your Metrics and expand the STOQ section.
3. Select Customer signed up for alert (STOQ) (or Stoq - Customer signed up for alert if you use an API key connection).
4. Click Save > Allow re-entry
5. A confirmation dialog appears — review the selected trigger and click Confirm and Save.

Note: Triggers cannot be changed once a flow is created. Double-check that you selected the correct metric before confirming.

Step 3: Add an Email Action

1. In the left panel, locate the Actions section.
2. Drag and drop the Email action into the flow, connecting it below the trigger.
3. Click the email action block to configure it.

Step 4: Configure Your Email Template

1. Set the subject line (for example, "We'll notify you when it's back in stock!").
2. Set the sender name to match your brand.
3. Click Edit Content to open the email template editor.
4. Design your email and insert dynamic variables from the STOQ metric using Klaviyo's template syntax.

To reference event properties in your template, use Klaviyo's variable syntax. For example:

• {{ event.product_title }} — inserts the product title
• {{ event.variant_title }} — inserts the variant name
• {{ event.image_url }} — inserts the product image URL
• {{ event.customer_name }} — inserts the customer's name
• {{ event.shop_name }} — inserts your store name

Tip: You can use the image_url property in an image block to show the exact product variant the customer signed up for. This makes the confirmation email feel personal and relevant.

Step 5: Review and Activate the Flow

1. After finishing your email template, click Review and Turn On in the top-right corner of the flow editor.
2. In the modal that appears, select Live from the dropdown.
3. Click Turn On to activate the flow.

Your flow is now live. Every time a customer signs up for a back-in-stock alert through STOQ, Klaviyo will send them your confirmation email automatically.

Ideas for Your Confirmation Email

Your confirmation email is the first touchpoint after a customer expresses interest in a product. Here are a few ways to make it count:

• Send a signup confirmation — Let customers know their alert signup was successful and that they will be notified when the item is back in stock.
• Suggest similar products — Recommend alternative items that are currently available, so the customer can shop now.
• Offer an exclusive discount — Include a coupon code as a thank-you for signing up.
• Welcome new visitors — If the customer is new to your store, introduce your brand and highlight popular products.

How to Test Your Flow

Before relying on your flow in production, verify that it sends emails correctly.

1. Go to the STOQ app in Shopify admin.
2. Navigate to Back in stock alerts > Reports > Current Waitlist.
3. Create a test signup or use an existing entry and click Send.
4. Check the email inbox for the test customer to confirm the email arrives and all variables are populated correctly.

Tip: In Klaviyo, you can also check the Activity Feed on a profile to see if the metric event was received and whether the flow was triggered.

Known Limitations

There are a few constraints to keep in mind when using this flow.

• The signup metric requires an active Klaviyo connection — either Sync to Klaviyo enabled or Klaviyo selected as your email provider in STOQ.
• The metric name differs depending on your connection method: Customer signed up for alert (STOQ) for OAuth, or Stoq - Customer signed up for alert for API key connections.
• Flow triggers in Klaviyo cannot be changed after a flow is created. If you selected the wrong metric, you must create a new flow.
• The image_url property may be empty if the product variant does not have an image assigned in Shopify.
• If double opt-in is enabled in STOQ, the optin_confirmed property may be false at the time of signup. The customer will need to confirm before receiving further marketing emails.

Troubleshooting

If your confirmation flow is not working as expected, check the table below.

FAQs

Q : Do I need to enable a separate setting in STOQ to send the signup metric?

A : No. The signup metric is sent to Klaviyo automatically once your connection is active. There is no separate setting required.

Q : What is the difference between the two metric names?

A : If connected using OAuth, the metric is named Customer signed up for alert (STOQ). If connected using an API key, it appears as Stoq - Customer signed up for alert. Both contain the same data.

Q : Can I change the flow trigger after creating the flow?

A : No. Klaviyo does not allow changing a flow trigger after creation. You will need to create a new flow and remove the old one.

Q : Can I send an SMS instead of an email?

A : Yes. You can add an SMS action in the flow instead of email and use the same event data to personalize the message.

Q : Will this flow conflict with STOQ's built in notification emails?

A : No. This flow sends a confirmation when a customer signs up, while STOQ sends notifications when the product is back in stock. Both work independently.

Q : Can I add a time delay before sending the confirmation email?

A : Yes. You can add a Time Delay step in the flow to send the email after a set duration.

Updated on: 10/04/2026