Every upsell needs a product source — the rule that decides which products appear inside the offer. You have three options, and each one fits a different style of merchandising. The setting is per-upsell, so different upsells can use different sources.
Option 1 — Manual selection
You hand-pick the products you want to show. Up to 20 products per upsell.
This is the most control: you decide exactly which items appear, in exactly the order you want, with the exact variants you want featured.
How it works
In the upsell form, set Product source to Manual selection.
Click the picker to add products from your catalog. You can add up to 20.
(Optional) For each product, pin specific variants — for example, only show the Medium and Large sizes, not the full range.
Drag the selected products to reorder them. The customer sees them in the order you set.
Save.
Variant pinning
For each product you add, you can either:
Leave variants empty — the product's default variant is shown to the customer. The variant selector still appears at checkout if there are alternative variants available.
Pin specific variants — only the variants you pin are offered to the customer.
Variant pinning is useful when:
You only want to surface in-season sizes
A product has many variants but only a few are upsell-worthy
You want the customer to choose between, say, "Black" and "Navy" without scrolling through eight other colours
Option 2 — Related items
Shopify maintains an automatic "Customers also bought" recommendations engine for every product in your store. With Related items, you delegate product selection to that engine — no curation required.
How it works
In the upsell form, set Product source to Related items.
Set Maximum number of products to show (between 1 and 10).
Save.
That's it. At runtime, Shopify picks the related items for the cart's anchor product and the upsell shows up to the maximum number you set.
What "anchor product" means
The recommendations are anchored on the product that's currently in the cart (for Checkout upsells) or the order (for Order-editing upsells). Different anchors produce different recommendations — the customer will see different items depending on what they bought.
Note: Shopify's recommendations engine returns at most 10 items, and the same anchor returns the same items consistently. If a particular anchor has no recommendations available, the upsell won't render for that customer.
Option 3 — Complementary products
Pulls from the pairings you've configured in Shopify's Search & Discovery app under "Complementary products". This is the merchant-curated equivalent of Related items: you've already told Shopify which products go together (e.g. "this phone case pairs with this phone"), and the upsell uses those pairings.
How it works
In Shopify admin, install the Search & Discovery app and configure complementary product pairings for the products you want to upsell from.
In the Triom upsell form, set Product source to Complementary products.
Set Maximum number of products to show (between 1 and 10).
Save.
When to pick Complementary products
You already manage cross-sell relationships in Search & Discovery
You want intentional pairings (not algorithmic recommendations)
You sell products with strong "X always goes with Y" relationships — phone + case, lens + lens cap, dress + matching belt
You want the same merchandising logic across your storefront and your upsells
Important: If you haven't configured complementary pairings in Search & Discovery for the cart's anchor product, no upsell will be shown for that customer. The source returns nothing rather than falling back to a default. If you start with this source, plan to set up pairings for your top products before launching.
A note on Order-editing upsells
For Order-editing upsells, the source applies to both surfaces (Thank You and Order Status) — you can't pick a different source per surface from a single upsell. If you want different source logic on each surface, create two upsells (one per surface) and use the Upsell ID pinning model described in Upsells in the Order-Editing Flow.
What's next
Choosing Who Sees an Upsell — narrow the audience for the products you've picked
Reading Your Upsell Analytics — see which sources convert best for your store