private TubeMQResult handleInvalidJson(String req) {
        LOGGER.warn("Invalid JSON format received: {}", req);
        return TubeMQResult.errorResult("Invalid JSON format.");
    }
Handles invalid JSON format in 'req' parameter.

@param req The invalid JSON format
@return TubeMQResult indicating an error
inlong-tubemq/tubemq-manager/src/main/java/org/apache/inlong/tubemq/manager/controller/topic/TopicWebController.java