Up to ten paid extras per set, on the products you pick
A catalogue product, or a service with no product behind it
Every price is rebuilt on the server, never sent by the browser
Free: no plan, no set cap, nothing held back
AddOnForge puts paid extras on the product pages you choose. A shopper ticks gift wrap, an extended warranty, assembly or anything else you sell, and each ticked extra reaches the cart as its own line at the price you set.
An extra is one of two kinds. It can be a real product from your catalogue, in which case stock, delivery and tax follow that product's own settings and your price replaces the catalogue price on that line. Or it can be a service with no product behind it, such as a warranty, which reaches the cart as a custom line with no stock tracked.
Prices are never decided in the browser. The page sends only identifiers and a quantity; the server reloads your set and rebuilds every line from the values you saved.
Once a shopper ticks an extra, the app shows its own add to cart button that adds the product and the extras together. Nothing is ticked to begin with, so a shopper who wants no extras never sees a second button. No app can hook into the product page's own add to cart button, so a shopper who ticks an extra and then uses that button gets the product without the extras.
Both catalogue versions are supported. No customer data is read or stored, and it is free.