Automatically add a product to the cart at checkout

Before you start

• Add the Rules Executor app block to your checkout. How to add it.
• The product must be for sale on your Online Store channel and in stock, or not tracking inventory. Shopify rejects cart changes for products buyers can’t buy.

Steps

Add a product

1. In Checkout Ninja, open Rules and click New checkout rule.
2. Enter a Title, up to 30 characters.
3. Under Condition, click Add condition and set when the product should be added. For example, Cart Total Greater Than 100.
4. Under Action, click Add Action and choose Modify Cart - Add Product / Update Product Quantity.
5. Choose Add Product.
6. Under Product Variant, select the product and the variant to add. If your selection has several variants, only the first is added.
7. Enter a Quantity. Leave it empty to add 1.
8. Keep Prevent adding duplicate products ticked. It’s on by default.
9. (Optional) Turn on Limit total quantity in cart and enter a Maximum quantity allowed.
10. Set Status to Active and click Save.

Set a product’s quantity

Use this to fix the quantity of a variant that’s already in the cart, for example to allow only one of a limited item.

1. Follow steps 1 to 4 above.
2. Choose Set Product Quantity.
3. Under Product, select the product and variant.
4. Enter the Quantity to set.
5. Set Status to Active and click Save.

How the add options work together

Prevent adding duplicate products	Limit total quantity in cart	What happens when the rule runs
On	Off	Adds the product once. Skips if the variant is already in the cart.
On	On	Same as above. The limit has no extra effect, because the product is never added a second time.
Off	On	Adds the quantity each time the rule runs, until the variant’s cart quantity reaches the maximum.
Off	Off	Adds the quantity every time the rule runs. Avoid this.

Verify it worked

1. Open your checkout with a cart that matches the rule. The product appears in the order summary.
2. Change something in the checkout, such as the shipping address. The product isn’t added a second time.
3. Test a cart that doesn’t match. The product isn’t added.

Limitations

• Shopify Plus only, because the rule runs in the Rules Executor checkout block.
• The product is added at its full price. Use a Shopify discount to make it free or cheaper.
• The product isn’t removed when the conditions stop matching.
• Set Product Quantity only changes a variant that’s already in the cart. It doesn’t add the variant. A quantity of 0 or an empty quantity is treated as 1, so this action can’t remove a product.
• The same variant is never added twice within 2 seconds, even with duplicates allowed. This stops double adds when the checkout updates quickly.

Troubleshooting

The product isn’t added. Check that the variant is available for sale and in stock, and that the rule is Active and the Rules Executor is in your checkout. With Prevent adding duplicate products on, nothing happens if the variant is already in the cart. Full checklist.

The wrong variant is added. The action uses the first variant in your selection. Open the rule, clear the Product Variant selection and pick only the variant you want.

Set Product Quantity does nothing. The variant isn’t in the cart. This action only changes existing lines. Pair it with an Add Product action, or a condition such as Variant in cart.