AddOnce lets merchants present optional products and services directly on the product page. Create a Companion Product once, then attach it to any product where it belongs. Because AddOnce uses native products, inventory, variants, and fulfillment continue to work as expected. Customers choose optional add-ons before adding to cart, and each item is added as its own native cart line.

• Add optional add-ons with native Shopify products
• Create once. Attach to unlimited products.
• Customers add each selection as independent Shopify cart lines
• Automatically supports single- and multi-variant companion products
• Theme App Extension with zero storefront impact until enabled