Unable to render preview for custom widget


This is a question related to creation of a custom Input Widget for additional form validation error. When I am working with the UI designer, I am able to set all its properties and see all the views but if I try to preview the same, I don't see anything. I am unable to fathom why this is happening.

Following is my template (I am not using any controller here. There is a custom asset that I added to add custom validations):

Problem starting a process forom a UI-designer button

I build a page with the UI-designer and I'm trying to set up a button to allow the user start a process from that page.
I got the process definition using the REST api: ../API/bpm/process?p=0&c=1&f=name=MiPrueba (process name MiPrueba), this is the result: