The mentioned checkbox solution is not what we want.
On the eCart support page, in the Archived Documentation section, see the "Building a Multiple Item Add to Cart Interface" tutorial:dataassist/
This will not work with the quantity boxes though, the quantities will need to be changed after the items are added to the cart.

Hi, I also need this. Can someone describe how to to it so it can work with quantoty fields an only one add to cart button? The mentioned checkbox solution is not what we want. Can someone do it for payment???
regards
jØ


