Which validation error message to use for user form?

1. What is the best way to show an error message when a user input some wrong data and submit?

What is the best way to show an error message when a user input some wrong data and submit?

Error messages should be clearly indicated

And you should be clear where that error has been made. You can do this by: Highlighting the field in question visually, usually with an outline around the input in a bright noticeable colour (usually red) Adding additional icons or visual cues to draw attention to the mistake.