React client-side iPart – added uber-simple React app to a page and it will not publish

Hi all,

I created the default dummy React app by doing: yarn create react-app dummyapp
…and didn’t change anything. It runs in the dev server on my local PC fine, of course.
I ran the command “yarn build”, and it creates a “build” folder.
I zipped up the “build” files and subfolder, uploaded the zip as a new client-based content type, and added that to a dummy content page. The page refuses to publish.

When I try to do it with a simple-ish working React app I created by coding along with a tutorial, the content page shows “there was a problem loading this area” in red, and it won’t publish either.

Neither of the above apps calls any webservice.

Does anyone have any ideas? Thank you!

React-y details:

The files I zipped in the first example are the “static” subfolder and 7 files: manifest.json, asset-manifest.json, index.html, an ico, 2 pngs, and robots.txt... nothing unexpected.
I followed the deployment instructions from the newer-look IMIS docs site:

a) Uploaded the zip file to RISE > Document System > iPartSource; clicked New > Zip File, navigated to and hilited zMikeReactExample.zip, entered description, clicked Upload.

b) Added a new content type: RISE > Maintenance > Content Types > select Custom folder.
New > Content Type > Client-Based, entered name & description, and, for the “URL to the html file that is used to display items of this type at runtime.”, ~iPartSource/zMikeReactExample.zip/index.html
I didn’t enter anything in the “URL to the html file that is used to configure content items of this type.” since the documentation says “URL to the config.html file that is used to configure content items of this type field, if you created one.”
Advanced Properties – left blank
Clicked Save. Just now double-checked, and it looks what should be normal.