Java code does not return any value, but shows scuessfull

Hi, I'm trying to run the below code
``
logger.info("START");
var composedRegMessage = Packages.scale.service.MessageComposerService.composeRegistrationMsg("id", "cd", "br", "num", false);
logger.info("Generated Message"+composedRegMessage);
logger.info("END"); ``

It just prints START and nothing, the response Code is JS-OK, how do I know what is happening, where can I find the logs and where the problem is.