code: public function setKeyAttribute($value)
      {
          // Key must be string
          if (!is_string($value)) {
              throw new \Exception('Invalid key type. Key must be string');
          }
  
          // Key must be below 129 chars
          if (strlen($value) > 128) {
              throw new \Exception('Invalid key length. Key must be below 128 chars');
          }
  
          $this->attributes['key'] = $value;
      }
docs: Key setter
  
  @param $value
  
  @throws \Exception