code: protected function errorMessage($filter, $field, $params = null)
      {
          $text = (isset($this->texts[$field][$filter]) && ! is_null($this->texts[$field][$filter])
              ? $this->texts[$field][$filter] : $this->msg);
          $text = str_replace([':label:', ':value:'], '%s', $text);
  
          if (! isset($this->data[$field])) {
              $this->errors[] = sprintf($text, $this->labels[$field], $params);
          } elseif (! is_null($params)) {
              if ($filter == 'matches') {
                  if ($this->matches($this->data[$field], $this->data[$params]) === false) {
                      $this->errors[] = sprintf($text, $this->labels[$field], $params);
                  }
              } else {
                  if ($this->$filter($this->data[$field], $params) === false) {
                      $this->errors[] = sprintf($text, $this->labels[$field], $params);
                  }
              }
          } else {
              if ($this->$filter($this->data[$field]) === false) {
                  $this->errors[] = sprintf($text, $this->labels[$field], $params);
              }
          }
      }
docs: Field validation error messages
  
  @param string $filter
  @param string $field
  @param string $params
  
  @return void