CMake seems to not integrate package into a dll correctly

Question

I wanted to create a dll to use cpp-packages in Dart. I was able to create the dll-file with CMake, but when I tried to open it in Dart it didn't work. In my cpp file I already had a function that when exported into a dll worked, but after I added another include-statement (#include <json/json.h>) and exported to a dll it didn't work anymore: The dll got compiled, but Dart couldn't open it anymore. This is the error I got in Dart:

Unhandled exception:
Invalid argument(s): Failed to load dynamic library './build/Debug/library.dll': error code 126
#0      _open (dart:ffi-patch/ffi_dynamic_library_patch.dart:11:43)
#1      new DynamicLibrary.open (dart:ffi-patch/ffi_dynamic_library_patch.dart:22:12)
#2      main (file:///C:/development/cpp/dll_libraries/library/main.dart:13:32)
<asynchronous suspension>

In my CMakeLists.txt-File I have the following Code:

set(JSONCPP_DIR "C:/development/cpp/packages/vcpkg/packages/jsoncpp_x64-windows")
set(JSONCPP_LIBRARY "C:/development/cpp/packages/vcpkg/packages/jsoncpp_x64-windows/lib/jsoncpp.lib")
include_directories($ENV{other_CPP_SDK_DIR}/include ${JSONCPP_DIR}/include)
target_sources(${LIBRARY} PRIVATE ${DEF_FILES})
target_link_libraries(${LIBRARY} PUBLIC ${other_libs} ${ADDITIONAL_LIBS} ${JSONCPP_LIBRARY})

I think the reason is, that Dart is not able to use the content of the package jsoncpp to execute the functions in the dll, but CMake compiled the dll.

I tried to inspect the dll, but everything seemed to be normal:

Dump of file build\Debug\library.dll

File Type: DLL

  Section contains the following exports for library.dll

    00000000 characteristics
    FFFFFFFF time date stamp
        0.00 version
           1 ordinal base
           2 number of functions
           2 number of names

    ordinal hint RVA      name

          1    0 0000F2BD init= @ILT+58040(?init@@YA_NXZ)
          2    1 0001F5FA writeDatabase = @ILT+124405(?writeDatabase@@YA_NXZ)

  Summary

        1000 .00cfg
      397000 .data
        A000 .idata
        2000 .pdata
      D8B000 .rdata
       49000 .reloc
        1000 .rsrc
     1713000 .text
        1000 .tls

Do you have any idea how I can fix this, so that Dart is able to open the dll?