GraalVM failed to create the method in generated .h file

Hi everyone,
I’m not sure if this is the place to ask this question but I saw few questions about GraalVm so I try to post my question anyway.
I would like to use GraalVM to call Scala classes into a C++ project. I managed to install everything from and create a native image exe (*.exe file from a jarfile which was obtained from sbt assembly) and it works as expected. Now, I’d like to create shared library from native image. I tested the example through this link (How to create a shared library from Java code | by Mitsunori Komatsu | Medium). I got all the files (.dll, .lib. .h etc). Unfortunately, I don’t have the add method in the generated .h file (<libfoobar.h>) as explained in GraalVM. Could someone try this example to see if the problem is in my side ? Thank you for your support.
Best regards