Knit does not charge a separate checkout. Shoppers pay in Shopify checkout. A Shopify Discount Function shipped with the app reads a hidden line-item property and applies the bundle reward.
You do not configure this per add-to-cart. You do need the Knit automatic discount to stay Active in Shopify admin → Discounts.
The line-item property
When a shopper adds a bundle, every line in that add carries:
The same value is on every line in the group. The Discount Function uses it to:
- Recognize which cart lines belong together
- Match the bundle version and tier
- Apply the percentage or fixed reward from that tier
If this property never reaches Shopify, items still sit in the cart at full price.
Where it can get lost
If a cart layer, middleware, or checkout app drops unknown line-item properties, the bundle discount will not apply. Keep __FB_ATC_UID.
Verify
- Add a bundle to cart from the widget.
- Complete a test order (or inspect the cart payload).
- In Shopify admin → Orders, open the order.
- Each bundle line should show
__FB_ATC_UID as a line-item property, and the discount should be on the order.
If lines are in the cart but the discount is missing, see Troubleshooting. 
