Troubleshooting

Use this page when the widget is missing, add-to-cart fails, or checkout does not show the bundle discount.

Checklist

Knit is installed and has been opened once in Shopify admin.
The bundle is Active and includes the product you are testing.
In Shopify admin → Discounts, the Knit automatic discount is Active.
You are testing a product that actually belongs to that bundle (product match or collection membership).
You waited up to 5 minutes after the last bundle edit (cache).

Symptom	Likely cause	What to do
Blank on a Liquid product page	Theme app extension not enabled, or product not in an active bundle	Enable the app embed in the theme editor. Confirm the bundle is Active and includes this product.
Blank iframe (headless / Tapcart)	Wrong `shop` domain, or embed origin blocked	Use `{store}.myshopify.com`. If the console says refused to connect, the host must allow `https://app.knit-bundle.co`.
”No bundle” / empty widget	No matching active bundle	Add the product (or its collection) to an Active bundle.
Headless JSON `APP_NOT_INSTALLED`	Storefront token not provisioned	Open Knit once in Shopify admin, then retry.
Headless JSON `INVALID_PARAMS`	Missing or invalid `shop`	Pass `shop=your-store.myshopify.com`.
Headless JSON `NOT_FOUND`	Headless not enabled on this deployment	Contact Knit support.
Stale products or old tiers	Cache	Wait up to 5 minutes, then reload.
Console `[nameless] RENDERER_THREW`	Renderer callback threw	Fix the JS asset. The last successful paint stays. See Renderer function.
Console `[nameless] RENDERER_LOAD_ERROR`	CSS fetch or JS `<script>` failed	Treat both assets as required. The widget does not render.
Console `[nameless] RENDERER_MOUNT_NOT_FOUND`	No `[data-nameless-block]` on the page	Enable the theme app embed.

On Liquid: confirm the theme is not intercepting the widget button, and that ATC override is only on if you intend the theme button to add the bundle. See Shopify integration.
On headless: you must handle addToCart over postMessage and reply with addToCartResult within about 10 seconds, or the widget shows CART_TIMEOUT. See Headless Bundles API.
On Tapcart: publish the app after adding the block, then test on a device, not only the static canvas.

Items can land in the cart at full price when __FB_ATC_UID never reaches Shopify.

Confirm the Knit automatic discount is Active in Shopify admin → Discounts.
Confirm the bundle is Active.
Add a bundle from the widget, then open the test order in Orders. Each bundle line should show __FB_ATC_UID and the discount.

Surface	What must happen
Liquid theme	The theme app extension adds the property. Do not strip line-item properties in cart apps.
Headless embed	Your `postMessage` handler must pass `attributes` through as Shopify line-item properties. See Headless Bundles API.
Tapcart	The Knit block adds the property. No extra merchant step.
Custom cart / Hydrogen	Your cart API must persist custom line-item properties all the way to checkout.

If a cart layer, middleware, or checkout app drops unknown line-item properties, the bundle discount will not apply. Keep __FB_ATC_UID.

Include:

Shopify domain (your-store.myshopify.com)
Product handle or ID
Endpoint URL or page URL
Full JSON error ({ ok: false, code, message }) or [nameless] / [knit-bundle] console logs
Screenshot or recording (storefront, Tapcart preview, or device)