A field guide to the 5 error messages every first-time deployer meets (and what they really mean)

You finally hit deploy. It worked on your laptop. Now it says one of these. 1. 'Cannot connect to localhost' Your app is still looking for a database on your own computer. The live server has to be told where the real one is. 2. 'Missing environment variable' A secret exists on your machine but not on the server. Add it in the host's settings, not in the code. 3. 'redirect_uri_mismatch' Google sign-in still thinks your app lives at localhost. Add your real domain to the allowed list. 4. 'Build failed' but it runs locally Your laptop has something installed or cached that the server doesn't. Check the Node or Python version first. 5. A blank white page The app loaded and then crashed in the browser. Open the console (F12), the red text there is the real answer. Almost all first deploys break on the same few things. What was your first one?