Online Manual / Configuration Files / Displaying an error message.

Command: errorMsg
Usage:

Allows you to display an error message to the user. It's recommended that you use this command with the if command.

Arguments:

• value="<text>"
  Specifies the error message to display.
  

Example:

if ("[output name='password1']" != "[output name='password2']") then errorMsg value="Your passwords do not match." endif

This example shows how to check if two password fields match. If they do not match, create an error message.