Errors displayed on the UI

Topic

How should we display errors to the users, if the communication ends abruptly, how should we show to the user that? Shall we use a toast, a banner, show it on the status bar, what else?

Context

The user should see whether its actions are invalid or whether a generic error occurred.

What you've tried

Mention any solutions or documentation you already checked.

Expected Outcome

The user should be able to see if SEGS got any errors on the UI, thanks to a visual clue present for a finite amount of time.