Node.js
A project usually contains package.json, optionally a lockfile and an entry file such as index.js. Check which file your service actually starts. The panel cannot automatically recognise an arbitrary application filename. List dependencies in package.json; for Cannot find module errors, check the package and installation output.
Python
The entry file is often app.py or your own configured filename. List libraries in requirements.txt. ImportError or ModuleNotFoundError usually indicates a missing dependency or a different runtime version. Check the available versions in service settings.
Variables and secrets
The Startup tab shows variables provided by the service template. It is not a universal vault for arbitrary secrets. Your own application can read a private file such as .env; it must support this explicitly. Do not upload the file to GitHub, and limit file-reading permissions. Anyone who can read code and configuration can usually retrieve the token too.
After changing configuration
Save changes and perform a controlled restart. Repeatedly pressing Start will not fix an error. Read the application output first.