Error message after form validation runs successful

Generally, if you want the message to be output by the form_helper's validation_errors() and/or form_error() functions, or via $this->form_validation->error() and/or $this->form_validation->error_string(), you will probably need to create a custom validation rule to run during validation.

Otherwise, you would simply handle the error the same way you handle a validation error. Generally, you would pass the error message through to the view and display it the same way you would a validation error.

Bonfire

Practical CodeIgniter 3
CodeIgniter Testing Guide