Show custom field for web form using dynamic forms

Summary

Show custom field for web form using dynamic forms

Content

Hi community, 

We want to use dynamic forms in order to show/hide custom filed when specific category is selected by the end user.

We went over the existing instructions Oracle has (link in below), made all the steps listed there ( uploaded needed files, (dynamic_ask.php, ect), install and activate new DynamicProductCategoryInput widget, deploy a new custom object, etx). But we reached a point where we do not now how to proceed: 

1. We already have custom fields that we want to show when specific category is selected on the webform. In the new custom object there are some default fields populated when custom object was deployed, and option to add new fields, but how do we add the ones we already have and want to use? For example, we have $paymentid custom filed, so from my understanding it needs to be included to List of Fields in Incident Object as it's shown in attached file. Is it the right flow?