Shopify Cart Transform Function not applying bundles/line merges — Functions, app, checkout extensibility.

Several products can look like “bundles / line merges never happen.” They do not share a settings panel. This page is only when a Shopify Cart Transform Function (cart.transform.run) should merge lines, expand a parent into components, or rewrite line properties — and the live cart / checkout still shows the untransformed lines. A missing PDP bundle builder / FBT widget is bundle builder not showing. Volume / quantity break / Buy X Get Y UI missing on PDP or cart is quantity breaks not showing. Script Editor line-item scripts after a Plus / Functions move is scripts not applying after Plus. An automatic discount Function that never reduces the total is Functions discount not applying. This page is only: Shopify Cart Transform Function not applying bundles/line merges (Functions, app, checkout extensibility).

Six ordinary reasons merges never fire: the Function is Draft / not deployed Active; the cart transform app is installed but not the selected transform for the shop; metafields / line attributes the input query expects are missing; checkout.liquid Scripts are still fighting checkout extensibility; a second cart transform or Bundles app overwrites the first; or you are debugging a missing theme widget / quantity-break UI / discount Function instead of cart.transform output. Walk them in that order. You already pay for Shopify + the app. You do not need another “bundle SaaS” to prove a Function that never runs.

In the Partner / custom app → Extensions, confirm the cart transform Function is deployed Active (not only preview). In Admin → Settings → Checkout (and Apps), confirm the cart transform app is installed and the shop’s selected Cart Transform is this Function — Shopify allows one active cart transform per shop. Screenshot the Active status and which app owns it.

Reproduce on the live storefront (not only theme preview): add the bundle parent / component SKUs the Function should merge. Capture Cart AJAX / Storefront cart JSON: line count, merchandise ids, properties, and whether components expanded or lines merged. If the PDP never shows a builder UI but cart.transform is fine, leave this page and use bundle builder not showing. If only the discount amount is wrong with lines already merged, open Functions discount not applying.

Confirm the product / variant metafields and cart line attributes your Function’s input query reads — missing namespace or storefront access means the transform silently skips merges. Redeploy after fixing the GraphQL input query. Require checkout extensibility for modern cart transforms; do not expect Script Editor line scripts to replace cart.transform.run after Plus / extensibility upgrades.

Disable a second cart transform, an old Bundles app that also rewrites lines, or leftover Scripts that fight merges. Retest guest and logged-in carts, Markets currencies, and draft vs live themes. If Script Editor still owns line changes after a Plus move, that is scripts not applying after Plus, not this Cart Transform playbook. If volume / BXGY UI is missing on the PDP while transform merges work, use quantity breaks not showing.

Checklist: (1) screenshot Cart Transform Function Active + selected app, (2) confirm metafields / line attributes the input query needs, (3) redeploy Function after input-query fix, (4) remove conflicting second transform / Scripts / Bundles rewriter, (5) confirm checkout extensibility (not checkout.liquid-only), (6) capture before/after cart JSON on live add-to-cart, (7) if only PDP widget or discount amount is wrong, switch playbooks.

Prove it: add the configured parent / components on the live storefront; cart shows the merged parent or expanded components with expected properties; checkout line items match cart; a second Markets locale still transforms. If lines merge but the automatic discount never applies, open Functions discount not applying.

Missing PDP bundle builder / FBT widget is bundle builder not showing. Volume / quantity break / BXGY UI missing is quantity breaks not showing. Script Editor line scripts after Plus / Functions migration is scripts not applying after Plus. Automatic discount Function not reducing totals is Functions discount not applying. None of those finish a Cart Transform Function that never merges or expands lines on the live cart.

Finish prove Active → fix metafields / input query / conflicts → live merge proof first. Only then open the related playbook that matches the remaining symptom.

Stay DIY if you can spend one afternoon on the list above: prove Cart Transform Active and selected, fix metafields / input query, remove conflicting transforms / Scripts, and stop treating bundle builder UI / quantity breaks / Scripts / discount Functions as the same bug. That is the whole playbook. No agency required. Short answers also live on the merchant FAQ. Related pages: bundle builder not showing, quantity breaks not showing, scripts not applying after Plus, Functions discount not applying.

Pay for help when the work is not the cart.transform JSON — it is connecting the stack you already have so lead capture is not dying in DMs, cart / ops exceptions land in a channel you already check, and the live store is one workflow instead of a spreadsheet plus a Slack bot you forgot. That is the Latch AI Ops install.

What $997 USD one-time buys: lead capture on the live store, ops alerts in a channel you already check, and a checkout-ready workflow. 72 hours after collaborator access, not after payment. One live Shopify store. Access plus a delivery thread. Store URL collected at checkout. Not a SaaS seat, not a Functions-agency retainer, not a conversion guarantee, not a brand or theme job.

Other shops’ public ranges, not testimonials: a checkout / ops install typically runs $500–$2,500. A full ops consulting block typically runs $2,000–$5,000. $997 is the cheap end of that work, sold as a 72-hour install of three systems — not as an earnings number or uptime claim.

What it does not buy: more orders, automatic Cart Transform quotas, a Plus license, or a case study. Latch AI Ops has not published customer proof because there are no customers yet. You are buying the install.

Checkout is on Whop. Operator is Nico. United States offer. You can revoke collaborator access after handoff. We do not take owner passwords.