If you encounter an error while using the Gmail application on your smartphone, switch to Gmail web browser to check if Gmail is working outside the application; this will determine if the problem persists with the application only or with Gmail overall. If still why is Gmail not working problem persists, check your browser’s extensions and temporarily remove or disable them to avoid conflicts with Gmail due to these. If that does not seem to be the problem as well, you can adjust the browser privacy settings.
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New York, Computer, Why Is Gmail Not Working?