'h5p utils pack' fails with “no valid libraries found; use ‘‑f’ to skip validation” – what am I missing?

I’m developing a custom H5P question type. My goal was to extend the existing H5P.Blanks question type and add Syntax Highlighting throught a thrid party packages from npm.

I am have problems packaging the library with the cli command h5p utils pack. 
I am getting a validation error, but I have no clue what is wrong with my library. I am guessing it could be something about having a build process that gets in the way of the command, but since all dependencies are listed in the library.json why would this be a problem? Other than that the library works fine, in the h5p-cli enviroment and when importet to Lumi H5P Desktop Editor.

The command I ran:
my_first_h5p_environment/libraries % h5p utils pack -r H5P.SyntaxBlanks syn.h5p
no valid libraries found; use '-f' to skip validation

Does anyone have a guess what could be wrong or what I am foolishly overlooking?
I already compared my implementation to other libraries and can't find a reason for this error.

My Code can be found here:
https://github.com/mohammed7700/bachelor-h5p-questiontypes/tree/main/H5P...

Any hint would be hugely appreciated. I’ve been been trying to find the root cause for quite a time now and feel I’m missing something obvious.