Call shoppers on the restock waitlist when their size comes back
Run a Loop Voice campaign to the shoppers who asked to hear about a restock, or start a flow from your restock app, and pace the calls to the units you actually have.
- Waitlist sign-upPhone number and call consent, by size
- Units landYou launch a batch sized to the stock
- First batch calledEarliest sign-ups, in local hours
- Variant link by textOpens on the size that came back
The short answer
A back-in-stock call tells a shopper on your waitlist that the item they asked about is back in their size, and texts the link while they're on the phone. Loop Voice doesn't list an inventory event among its triggers, so the call starts from the waitlist: a campaign to a Klaviyo or Shopify segment of sign-ups (campaigns are in beta), or a flow started from a CSV upload, the added to list trigger, a custom event or a restock app connected through Zapier. We have no back-in-stock results to publish yet.
What a call sounds like
Loop Voice agent
Illustrative conversation
Agent
“Hi Marcus, it's Alex, an AI assistant calling from [Store]. If you'd rather not get these calls, just say stop. You asked us to tell you when the Ridge trail shoe came back in 10.5 wide. That size came in this morning, and we're calling the waitlist first. Should I text you the link to that size?”
Customer
“Yes, please. Did they change the fit from last year's pair?”
An illustration, not a recording. Real calls are in the call library.
Klaviyo's back-in-stock flow notifies everyone on the list at once unless you set up batches. When 40 pairs of one size come back for 600 people, the shoppers who waited longest can find it sold out by the time they open the email, and any call placed after that point is about something you no longer have.
When it works, and when to skip it
Works well for
- Products that sell out by size, color or version, with the waitlist kept per variant.
- Short runs against long lists, where the people who waited longest should hear first.
- Higher-priced restocks where one question decides the order: did the fit change, is this the new version, when is the next run.
- Waitlists collected with a phone number and consent to calls (calling rules).
Skip it for
- Deep restocks that everyone on the list can buy. The email covers those for less.
- Lists collected through an email-only form, or with an SMS opt-in that says nothing about calls.
- Low-margin items, where a few answered calls cost more than the sale earns.
- Stock that hasn't landed. Call when the units are on your shelves and live on the site, not when a shipment is due.
Set it up in Loop Voice
Collect call consent on the waitlist form
Add a phone field and an unchecked box that names your store, covers calls made with an AI voice and says agreeing isn't a condition of purchase. Keep each sign-up's date and variant with it.
Choose how the list gets in
Run a campaign to a Klaviyo or Shopify segment of the people waiting on the item, or start a flow from a CSV upload, the added to list trigger, a custom event, or your restock app through Zapier.
Brief the agent on what's back
Load the product details and what changed since the last run, and write down the stock facts that stay true all day, such as which sizes came back. Leave live counts out.
Pick the calling window and pace
Set when and how fast: the campaign's time zone, its daily calling window and calls per minute. Do-not-contact numbers are dropped before the first dial, and a long list can run past one day.
Launch in batches
Split a long list by sign-up date, check each batch's credit estimate against your balance, and launch the next batch only after you've checked what's left in stock.
Compare the batches
Each campaign reports its own calls, with orders matched to calls by Shopify order number, so you can see whether early sign-ups bought more often than late ones.
Settings that decide a restock campaign
Campaigns are in beta. These are the settings that keep the calls in step with your stock.
- Audience
- The shoppers waiting on the variant that came back, as a Klaviyo or Shopify segment. If a segment can't isolate the size, export that size's list and start a flow from a CSV upload instead. Add a condition that leaves out anyone who has ordered the item since signing up, and check the member list right before launch.
- Consent condition
- Loop Voice doesn't read Klaviyo's consent flags, so put the call-consent condition in the segment itself.
- Pace
- Calls per minute, inside a daily window that applies in each shopper's local time. The batch size keeps calls within the stock; the pace only decides how fast a batch finishes.
- Stop conditions on flows
- A flow stops when the customer places an order, so a shopper who buys from the email while waiting for the call step isn't called. Take anyone who bought before you uploaded the list out of the CSV.
- Objectives and guardrails
- Leave create urgency off: the honest urgency in a restock is that the waitlist hears first, and that belongs in your instructions. Keep the never hallucinate guardrail on.
Keep the waitlist by size
Klaviyo ties each back-in-stock sign-up to a catalog variant, and a shopper can wait on as many variants as they like (Klaviyo developer docs). Use that, and call by variant.
Text a link that opens on the size, not just the product page. On Shopify that's a variant deep link, the product URL with ?variant= and the variant's ID, which Shopify's theme guidance uses to show that variant as selected (Shopify docs).
Example: a jacket comes back in medium and large only. The waitlist holds 900 people across five sizes, 310 of them on medium or large. Those 310 get a call; the other 590 hear nothing until their size is back.
Pace the calls to the stock
Klaviyo paces its own back-in-stock emails against inventory: a Restock minimum sets how many units must be in stock before anyone hears, batch settings notify a set number of subscribers per unit in stock, then wait a set interval, and stock is counted again at the end of each wait (Klaviyo). A Loop Voice campaign paces by calls per minute, not by units in stock, so you size each batch by hand.
Example: 40 pairs of a size 9 are back and 600 people are on that size's list. In Loop Voice's September 2026 benchmark, 15.9% of shoppers called picked up at least once, often after several attempts. At that rate, calling all 600 means about 95 conversations for 40 pairs. Call the first 200 sign-ups, about 32 conversations, and check stock before the next 200.
Let the ratio decide which channel goes first. When units are few against the list, call first so the earliest sign-ups hear before the email goes out. When there's enough for everyone, the email may be all you need; if you call too, send the email first and call a day later, to a segment that leaves out anyone who has ordered the item since.
Say only what's true about stock
The FTC's staff report on dark patterns lists "saying inventory is low when it isn't" as a way of pressuring buyers, with "Only 1 left in stock" as its example (FTC). A call can make the same mistake out loud.
Give the agent facts that stay true for the whole campaign: which sizes came back, that the waitlist hears first, and when the next run is due if you know it. A count you write into the instructions doesn't update itself, and product documents in the knowledge base refresh nightly, not by the minute.
Example: "Size 9 came back this morning, and we're calling the waitlist first" stays true while the batch runs. "There are only a few left" might stop being true by lunch.
Build a waitlist you can call
Where the list lives decides the route in. Klaviyo's help center lists Shopify among the platforms its back-in-stock flows support, and WooCommerce isn't on that list (Klaviyo). On WooCommerce, check before you rely on it, or keep the list in a restock app and send it in as a CSV or through Zapier.
Keep the sign-up date on every entry. It makes first come, first called possible, and it lets you set an age limit, so a shopper who signed up a year ago isn't the first one you call.
Built for the questions between intent and action
Fit and version questions
How the size runs and what changed since the last batch, answered from your product details.
The variant link
Texted during the call, opening on the size that came back.
Changed minds
If the shopper has moved on, the agent thanks them and ends the call. Asking for no more calls puts the number on the do-not-contact list.
Results by batch
Calls and attributed orders for each campaign, so early and late sign-ups can be compared.
No back-in-stock numbers yet, so track each batch
Loop Voice's September 2026 benchmark doesn't report restock calls on their own, so there's no restock rate to quote. Track these on every batch:
- Answer rate
- Shoppers who picked up, out of everyone called. Size the next batch from your first one, not from the 15.9% benchmark figure.
- Orders per shopper called
- Attributed orders from the batch divided by shoppers called, compared across early and late sign-ups.
- Calls after sell-out
- Calls that offered a size that was already gone. The target is zero.
- Opt-outs
- Shoppers who asked for no more calls. If the share climbs, check how old the list is and what the sign-up form promised.
Source: Loop Voice Ecommerce Benchmark
Works with
Common questions
Can Loop Voice call shoppers the moment an item is back in stock?
Not from your inventory: there's no inventory event in Loop Voice's trigger list. Launch a campaign when the units land, or start a flow from your restock app through Zapier or a custom event, if your app can send one.
How do we avoid calling about a size that already sold out?
Call by variant, in batches sized to the stock, and check what's left before each batch. On a flow, an order placed before the call step stops the flow, so a shopper who buys from the email in the meantime isn't called.
What can the agent say about how much stock is left?
Only what stays true for the whole campaign, such as which sizes came back today. Counts go stale, and the FTC's staff report on dark patterns names false low-stock claims as a pressure tactic.
Can we call shoppers who joined the waitlist with only an email address?
No. Without a phone number and consent to calls, the email is their notice. Put a phone field and a consent box for calls on the form before the next restock.
Can the agent hold an item for a shopper on the waitlist?
Not on the call. The agent texts the link and the shopper checks out on your site like anyone else, so tell it never to promise to hold one.
Does signing up for a restock alert count as consent to calls?
Only if the form said so. A restock call promotes a product, so treat it as a marketing call that needs prior express written consent to AI-voiced calls. The calling rules guide shows what the form should say; have counsel check yours.
Read more before you set it up
- Win-Back and VIP Calls: Who to Call, What to Offer, What to SaySegment building, consent checks and a holdout for calls to a defined list.Read
- Is It Legal to Call Abandoned Carts? TCPA Rules for AI CallsThe consent wording a waitlist form needs before anyone calls it.Read
- Klaviyo Abandoned Cart Flows and Phone Calls: A Timing PlanWhy Klaviyo can't see a text Loop Voice sent, and how to pick one system to send it.Read
- Email vs SMS vs Calls for Abandoned Carts: How to Run All ThreeOne owner for timing, caps and stop rules when email, texts and calls reach the same shopper.Read
Keep the conversation moving
Ready to launch back-in-stock calls?
Setup takes under 10 minutes. No code, no headcount.