This guide is for ecommerce, CRM and IT leads at Australian retailers who run Shopify Plus with Klaviyo and connect both to an ERP, a PIM, a loyalty platform or an integration layer. It lists the flows to check, what breaks under peak load, and the Australian rules that apply to peak-season email and SMS. Vendor limits were checked on Shopify's and Klaviyo's own pages on 30 October 2026.
How big is the peak this year?
Big enough that small failures cost real money. The Australian Retailers Association and Roy Morgan forecast a record A$6.8 billion over the four days of Black Friday to Cyber Monday in 2025, up 4% on 2024. Australia Post delivered almost 111 million parcels in November and December 2025.
On the platforms themselves, Shopify merchants sold US$14.6 billion over BFCM 2025, peaking at US$5.1 million a minute, and Australia was the third-highest-selling country after the US and UK. Klaviyo sent more than 22.7 billion messages for its customers over the same weekend. Email and text drove 42% of their total revenue, rising to 43% on peak days.
For 2026, the dates are Black Friday on 27 November and Cyber Monday on 30 November. Click Frenzy's main event already ran from 27 to 30 October. Christmas then brings Australia Post's parcel cut-offs: Tuesday 22 December for Parcel Post within a state, and earlier interstate and to Western Australia.
Which data flows matter most at peak?
Six flows carry most of the revenue and most of the risk. For each one, decide which system owns the data, then test the failure case, not just the happy path.
| Flow | Owner of the data | How it moves | What breaks at peak | Check before your freeze |
|---|---|---|---|---|
| Orders and checkouts into Klaviyo | Shopify | Native integration, real time | Abandoned-checkout flows miss people who never gave an email or phone number | Test a full checkout on your live theme and checkout extensions |
| Product catalog and stock | ERP or PIM, then Shopify | Integration layer into Shopify, then native sync to Klaviyo | Sale categories lag; back-in-stock emails go to sold-out items | Load sale collections early; know the 6-hour category sync |
| Email and SMS consent | Shopify checkout and Klaviyo forms | Native sync, two-way if enabled | SMS subscribers imported from elsewhere aren't marketable | Count SMS-consented profiles in both systems and reconcile |
| Orders into the ERP and warehouse | Shopify | Webhooks or polling via middleware | Endpoint outages remove webhook subscriptions; orders stop flowing | Monitor the subscription, not just the endpoint; run a reconciliation job |
| Custom events (loyalty, returns, ERP status) into Klaviyo | ERP, loyalty or returns platform | Klaviyo API from middleware | 429 errors drop events if the code doesn't retry | Retry with backoff; queue, don't discard |
| Promotions and pricing logic | Shopify | Shopify Functions and discounts | Old Shopify Scripts no longer run | Confirm every discount was rebuilt and tested |
Our Shopify Plus and Klaviyo teams start every peak review with this table. The rest of this guide explains each check.
What does the native Klaviyo–Shopify sync handle, and where are its gaps?
The native integration handles the core well. On connection, Klaviyo syncs the last 90 days of orders and customers first, then older history. After that, new data syncs in real time. Placed Order and Ordered Product events arrive seconds apart, so Klaviyo recommends triggering flows and segments on Placed Order consistently.
The gaps are specific and worth knowing before peak:
- Abandoned checkouts need contact details first. Klaviyo only records Checkout Started once Shopify sends checkout data with a valid email address or phone number. On a customised checkout, a shopper may need to reach the next step first. If you changed checkout extensions this year, test the abandoned-checkout flow end to end.
- Category changes lag. Catalog items sync in real time, but new categories and category membership sync every 6 hours. You can't resync a whole catalog at once, and only one catalog resync runs at a time. Build Black Friday collections days before the sale, not on the night, if emails or feeds depend on them.
- Events don't update after the fact. Later changes to an order event aren't re-synced, and profiles deleted in Shopify aren't deleted in Klaviyo.
- SMS consent syncs only for first-time subscribers. Klaviyo syncs SMS consent from Shopify only when someone subscribes to SMS in Shopify for the first time. Subscribers collected elsewhere need a separate import with their consent records.
- One store per Klaviyo account. Klaviyo supports one integration of each type per account, so expansion stores for New Zealand or other markets need their own Klaviyo accounts and their own checks.
Why do webhook flows to the ERP fail at Black Friday?
Because the failure is silent. Most retailers send Shopify orders to their ERP, warehouse or 3PL through webhooks handled by middleware such as n8n, Celigo or custom code. Shopify's rules are strict:
- Your endpoint must respond within five seconds or the delivery fails.
- Shopify retries a failed delivery up to eight times in four hours. If failures persist, it removes the subscription.
- Shopify doesn't guarantee ordering or delivery. It tells developers to ignore duplicates using the
X-Shopify-Webhook-Idheader and to run reconciliation jobs that fetch data from Shopify on a schedule.
Put those together on Black Friday. A middleware endpoint that slows under load starts missing the five-second window. If it's down for more than four hours overnight, the subscription can disappear, and new orders simply stop arriving in the ERP. Nothing errors in Shopify, and the storefront keeps taking orders.
Three controls prevent it. Acknowledge the webhook immediately and process it from a queue. Alert when a subscription disappears, not only when the endpoint is down. Run an hourly reconciliation job during peak that compares Shopify order counts with the ERP's.
Will Shopify and Klaviyo API limits slow us down?
Not if the integration is built to respect them. Shopify Plus stores get 1,000 points a second on the GraphQL Admin API, ten times the standard plans' 100. A single query can't cost more than 1,000 points. The REST Admin API is legacy as of October 2024, so stock and price syncs still written against REST are worth reviewing before next year's peak.
Klaviyo's API uses per-endpoint rate tiers, from 1 request a second (XS) to 350 a second burst and 3,500 a minute steady (XL). When you exceed one, Klaviyo returns a 429 error with a Retry-After header, and recommends exponential backoff with jitter. As an illustration, if a loyalty platform pushes 20,000 points-balance events at once to an endpoint in the XL tier, they take about six minutes at the steady rate. Code that retries finishes the job. Code that treats a 429 as a failure drops thousands of events, and the flows that depend on them never fire.
Check which tier each endpoint you call sits in. Klaviyo also retires old API revisions two years after release: revision 2024-10-15 reached the end of its support on 15 October 2026. If a custom integration pins an old revision, upgrade it now rather than in the middle of peak.
Are our promotions still running on Shopify Scripts?
They shouldn't be. Shopify Scripts stopped running entirely on 30 June 2026, replaced by Shopify Functions. Any tiered discount, gift-with-purchase or shipping rule that lived in a Script has either been rebuilt as a Function or a discount, or it no longer applies. Test every Black Friday promotion in checkout before the freeze, including how it interacts with codes sent from Klaviyo.
For simpler automations, Shopify Flow is free on Plus. Its Klaviyo connector now has one action, "Track an event", since Klaviyo retired the "Create a campaign" action on 16 October 2025. Flows built on the old action need rework.
How do we protect deliverability when volume spikes?
Ramp up early, from your engaged audience out. Klaviyo's BFCM guidance is to start two weeks out and grow each send's audience by about 50% until you reach just under your total emailable profiles, then pull back to engaged profiles for a few days before the big send. Large lists may need longer. For Black Friday on 27 November, that ramp starts by 13 November.
As a worked example, a retailer whose engaged audience is 40,000 profiles and whose full emailable list is 200,000 would send to 40,000, then 60,000, 90,000, 135,000 and finally just under 200,000. That's five sends before the full-list send is routine.
Mailbox providers set the hard limits. Senders of more than 5,000 messages a day to Gmail accounts must authenticate with SPF, DKIM and DMARC, offer one-click unsubscribe, and keep spam rates below 0.30% in Postmaster Tools, with Google advising below 0.10%. Yahoo's rules are similar and expect unsubscribes honoured within two days. Klaviyo counts transactional email towards the 5,000 threshold and requires a branded sending domain for bulk senders.
Klaviyo's Smart Sending skips anyone who received a message within the window: 16 hours for email and 24 hours for SMS by default. It's on by default for campaigns but not for every flow. Decide deliberately whether your Black Friday flows should respect it.
Which Australian rules catch retailers at peak?
Three regulators matter, and each has acted on peak-season behaviour.
The Spam Act and order emails. The ACMA penalised Lululemon A$702,900 in March 2026 for more than 370,000 shipping and order-confirmation emails sent between 1 December 2024 and 5 January 2025. The emails carried promotional content but no unsubscribe. If your Shopify or Klaviyo order emails include product recommendations or offers, they need a working unsubscribe. The ACMA's Spam Act guidance also requires consent you can prove, sender identification, and unsubscribes honoured within five working days.
SMS sender IDs. Since 1 July 2026, texts sent with an unregistered alphanumeric sender ID are labelled "Unverified" by the carrier and grouped in one thread. Businesses register through their telco or messaging provider. Check that the sender ID used in Klaviyo SMS is registered before your Black Friday texts go out.
Sale claims and countdown timers. The ACCC's review of Black Friday 2025 found that about half of the 50 retailers it checked made concerning claims, including false countdown timers. In September 2026 James Lane and Vuly paid penalties over sales that ran past their advertised end dates. Countdown timers in Klaviyo emails and "ends tonight" flows have to match what the store actually does.
Privacy rules apply too. From 10 December 2026, organisations that use personal information in automated decisions that could significantly affect people's rights or interests must describe them in their privacy policies. Our guide to automated decisions and the Privacy Act covers what that means.
What should we do before the freeze?
Work through this list before your change freeze, ideally by Friday 13 November:
- Map the six flows in the table above, with an owner for each and a named person on call over the weekend.
- Test the failure cases. Take the middleware endpoint down in staging and confirm the alert fires. Run a checkout with no email until the last step.
- Reconcile consent. Compare email- and SMS-consented counts in Shopify and Klaviyo, and import any SMS subscribers the native sync missed, with their consent evidence.
- Load sale collections and catalog changes early, allowing for the 6-hour category sync.
- Check every API integration for 429 handling, retries and a current Klaviyo API revision.
- Start the sending ramp and confirm SPF, DKIM, DMARC and one-click unsubscribe on your branded domain.
- Check compliance: an unsubscribe in any order email with promotional content, a registered SMS sender ID, and honest countdown timers.
- Set up monitoring: webhook subscription status, hourly Shopify-to-ERP order reconciliation, and Klaviyo flow trigger counts compared with orders.
Integration gaps like these are the work we do as an integrator for the gaps between platforms. For bigger questions about how Klaviyo, Shopify and your CRM share one customer record, see our single customer view guide, and for planning a move off Marketing Cloud, our guide to migrating from Salesforce Marketing Cloud to Klaviyo. Our connected enterprise guide covers choosing an integration layer, and the Myer case study shows segmented, personalised email at a scale of 1.4 million recipients.
Frequently asked questions
Does Shopify Plus give us more API capacity for Black Friday? Yes. Plus stores get 1,000 points a second on the GraphQL Admin API, against 100 on standard plans and 200 on Advanced. Capacity is still per app per store, so an inefficient integration can use it up.
Should our order confirmation emails come from Shopify or Klaviyo? Either works, but pick one and make sure nobody gets two. If they include promotional content, they need an unsubscribe under the Spam Act, whichever system sends them.
When should we freeze changes? Most retailers freeze integration and checkout changes about two weeks before Black Friday, which this year means Friday 13 November. Content and campaign changes can continue; code and integration changes shouldn't.
Get a peak-readiness check
If you'd like a second pair of eyes on your Shopify Plus and Klaviyo data flows before the freeze, talk to our team. We'll review the six flows above, test the failure cases with you, and tell you plainly what to fix first.
