I\'m using a java jar to send and receive messages using Chrome Native Messaging.
I enabled logging of Chrome so I could read C:\\Users\\%UserName%\\AppData\\Local
Many answers suggest checking the correctness of processing the first four bytes. But this is not always the real reason. It seems that in your case the reason is the absence of an @echo off in launch.bat.
When an error occurs
Native Messaging host tried sending a message that is 977472013 bytes long
First of all, try to start the application from the command line, it is possible that the output is "trash"