Ninja Forms (or Other) with FrontStream Payments

I am trying to use Ninja Forms as a registration for workshops I run. I have used Frontstream payments as my card processor (in connection with a Godaddy shopping cart) for ages and would like to keep it as my card processor but move to a registration tool with more flexibility and wordpress compatibility.

Frontstream’s virtual terminal (Fasttransact) provides tools to create html forms and buttons but I just don’t know how to make them work with my form.

The basic idea of my registration form is here: https://vivaceproductions.com/test-page/

And all the tools and documentation from Frontstream can be found here:
https://vivaceproductions.com/shared-references/

Any plugins / extenstions / coding I can do?