Then, you need to pass your containers (in case you add a new container) to
or simply to the column of an existing container (in case you don't create a container of your own to hold the fields). Anyways make always sure, that your generated JSON is correct.
Also, this approach does not support saving the form (at least not your dynamically added fields). To do that, you will need some hack to accieve this, like saving all properties into a hidden text field that holds all your values or manually use task variables which are also not that easy to do...