Doesn’t seem to work – at all!

I can’t seem to even get started with your plugin – which seems to have so much potential!
When initially opening a form, I believe I’m supposed to see some form fields on the left side of the page, containing things that I can drag and drop onto the form canvas. Unfortunately, this is what I currently see: https://i.imgur.com/VB89h3L.png
I’m running WP 5.0.3 and perhaps this is the root of the problem, since it appears you’ve only tested to pre-v5.