Where is application error logs stored?

[B-Esmaili]

Some of my website's users reported a bug telling me they keep getting "An unexpected error has occurred" error.I couldn't find any way to get exception detail from their devices.The only thing come to mind is checking application error log file to get stack trace, but couldn't find nextjs error log file either.could you please tell me how can i debug my application?

[timneutkens]

Error logs are output to stderr. If you are hosting on zeit.co you can go to <yourdomain>/_logs