The Checkout upsell puts recommended products inside Shopify’s own checkout, where the shopper has their payment details out and one tap adds an item to the order they are already placing.
Checkout upsells require Shopify Plus. Shopify only allows apps to add blocks to checkout on Plus. The card is visible in the CartSella upsell picker on every store, but it cannot be opened without Plus. Every other upsell type works on every plan.
Shopify checkout with a CartSella block above the order summary offering a matching product with an Add button

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Where the shopper sees it

Inside checkout, at whichever spot you place the app block in Shopify’s checkout editor. Common spots are above or below the order summary, and after the shipping method. The look, fonts and colours come from your Shopify checkout branding. That is Shopify’s rule, not ours, and it is a good one: an upsell that matches the checkout gets tapped, one that looks bolted on gets ignored.

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Pick a style

CartSella asks for a style the moment you create the upsell. You can switch it later in the editor.

Product recommendation

Suggest products, hand-picked or automatic, with an Add button and an optional variant selector.

Subscription upgrade

Offer your products with a “subscribe and save” toggle. The saving comes from your subscription app’s selling plans.

Cross-sell

Recommend products that go with what is already in the cart, hiding anything the shopper has already added.
The choose a checkout style modal with the three style cards: Product recommendation, Subscription upgrade and Cross-sell
The Subscription upgrade style has no Discount section. Its saving is whatever your subscription app’s selling plan offers, so a CartSella discount on top would be a number nobody honours.

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Set one up

1

Create it

Upsells → Create upsell → Checkout upsell, then pick one of the three styles.
2

Name it

The Storefront title is the heading shoppers read in checkout. Add dates if it is seasonal.
3

Choose when to show

Always, above a cart total, or only when a specific product is in the cart.
4

Pick the products

Manual or Auto.
5

Save and copy the ID

The sidebar shows the Upsell ID with a Copy ID & open checkout editor button.
6

Add the block in the checkout editor

In your Shopify admin, go to Settings → Checkout → Customize. Click Add app block where you want it, choose CartSella checkout upsell, paste the ID into the block’s Upsell ID field, and click Save.
The Shopify checkout editor with the CartSella checkout upsell app block selected and its Upsell ID setting visible
Leave the block’s Upsell ID blank and the block shows the highest-priority checkout upsell that qualifies for that cart, whichever style it is. Paste an ID and the block is pinned: it shows that upsell or nothing at all, never a substitute.

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When to show

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Products to recommend

Hand-pick products or variants. Best for a small, high-margin set of add-ons.

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Checkout display

This section is where the copy and the toggles live. Colours and fonts are not here, because checkout branding owns them.
The Checkout display section of the checkout upsell editor showing the three style cards, subtitle, add button label and show-element checkboxes

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Eligibility and advanced

Eligibility & targeting offers Traffic source, Customer tags, Customer location and Markets (the last only when your store has more than one market).
Customer rules are checked properly at checkout, because by then Shopify knows who the shopper is. A shopper who does not qualify simply does not see the block. This is stricter than the storefront, where a customer tag rule never hides anything from a guest.
Advanced options:
  • Priority, 1 to 10, default 5. Decides which checkout upsell an unpinned block picks.
  • Maximum uses, total and per customer. See Advanced offer settings.
  • Exclude products already in cart, with Match recommended product variants as a sub-option. The Cross-sell style hides already-added items on its own regardless.
There is no subscribe and save toggle here. The Subscription upgrade style is the checkout’s version of it.

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Discount

Fill one in and the product is still shown at its normal price, unless you are using the Subscription upgrade style, which has no Discount section at all. CartSella does not advertise a discount the checkout will not honour. For a real discount, create an offer and let the upsell recommend the product.

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Limits and gotchas

  • Shopify Plus only. There is no workaround. On other plans, the closest equivalents are the Post-purchase upsell, which works on every plan and does apply a discount, and the Cart upsell.
  • Drafts never render. Set the status to Active and save before pasting the ID.
  • The block is in the checkout editor, not the theme editor. If you cannot find it, you are in the wrong editor.
  • One block, one upsell. Adding the same block twice with two IDs works, but two upsells in one checkout is usually one too many.
  • If you pinned an ID and nothing shows, the upsell is probably a draft, out of schedule, or its condition does not match that cart. A pinned block never falls back to a different upsell.