Manifest.json issue maybe more?

[BarryCarlyon]

If you have changed the settings on Twitch Developers for an extensions Asset Hosting you may need to refresh manifest and recreate any views you have.

@camskernel

But maybe I am missing something here, if I would normally run my app by doing npm install then npm start on both the backend and front end, is npm start what I want to put as my commands?

So you are attempting to use:

Did you enter the path as well as a host command?