Help · When something is wrong
The build worked, so the problem is in how the app starts or which port it listens on.
The build succeeded, so your code is valid and its dependencies installed. Something goes wrong after that — when we actually start the app.
Open the app and look at the logs. They show what your app printed as it tried to start, and the reason is nearly always there.
It listens on the wrong port. This is by far the most common. Your app must use the port we give it in the PORT environment variable, not a fixed number. In Node that is process.env.PORT; in Python, os.environ["PORT"]. Keep your old port as the fallback and it will still work on your own machine.
It crashes immediately on starting. The logs will show the error. A missing environment variable — an API key you have on your own machine but never added here — is the usual culprit. Add it under the app's secrets.
It is not a web app at all. A script that runs once and finishes has nothing for a browser to connect to. If you want something that runs on a schedule rather than answering visitors, that is a scheduled task, not an app.
It takes too long to start. If your app needs more than a few seconds before it can answer, it may be marked as failed. Move slow work to after it starts listening.
That is usually a missing file — a stylesheet or image that exists on your machine but was not included in what you uploaded. Check the upload actually contained every folder.
Send us the app name. We can see the same logs you can, and we would rather look than have you guess.
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