Hello,

Regrettably, there is no native support for this. However, you can implement a custom shopping cart provider for that (please take a look into the CustomShoppingCartInfoProvider section). You can check the current shopping cart for all it's content and if there is the item A in it, just add the item B to it. This you can specify within the EvaluateShopping cart method. For more information please check also the following knowledge base article about Adding products to shopping cart using our API.

Best regards,
Boris Pocatko