You're using a “Log Message” action, but what you want to use to show something to the user you'll either want to use a “validation feedback” action or a “show message” action. Validation feedback shows up on a field of your choice (so for instance, login name), and a show message action is a pop-up. In your case, validation feedback will probably be best for the user experience.
I`ve changed the log message for a validation message and it´s works perfectly.
Thank you very much.