i got this error in the log console when the system was trying to start the app, as it automatically seems to (and presumably had an invalid start script in the package.json).
to explain: i’d cloned a git project that was a static site really (but had a package.json due to maybe some webpack or build pipeline stuff)… presence of package.json seems to be the thing that makes glitch treat project as server-based not static.
the problem was fixed/worked-around in my case by deleting the package.json which meant that glitch would serve as a static site.