If you're having trouble with NCM2, Please provide the following information
along with your detailed issue description:

OS

Windows 10

(If you're using Linux, sharing a reproducible, vimrc minimized docker image,
can definitely help solving the issue)

neovim :version output

:version NVIM v0.3.8 Build type: RelWithDebInfo LuaJIT 2.0.5 Compilation: C:/Program Files (x86)/Microsoft Visual Studio/2017/Community/VC/Tools/MSVC/14.16.27023/bin/Hostx86/x64/cl.exe /DWIN32 /D_WINDOWS /W3 /MD /Zi /O2 /Ob1 /DNDEBUG -DMIN_LOG_LEVEL=3 /W3 -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_DEPRECATE -DWIN32 -D_WIN32_WINNT=0x0600 -DINCLUDE_GENERATED_DECLARATIONS -DNV
IM_MSGPACK_HAS_FLOAT32 -DNVIM_UNIBI_HAS_VAR_FROM -IC:/projects/neovim/build/config -IC:/projects/neovim/src -IC:/projects/neovim/.deps/usr/include -IC:/projec
ts/neovim/build/src/nvim/auto -IC:/projects/neovim/build/include Compiled by appveyor@APPVYR-WIN Features: -acl +iconv -jemalloc +tui See ":help feature-compile" system vimrc file: "$VIM\sysinit.vim" fall-back for $VIM: "C:/Program Files/nvim/share/nvim" Run :checkhealth for more info

Minimal vimrc for reproducing the issue

    " assuming you're using vim-plug: https://github.com/junegunn/vim-plug
call plug#begin(stdpath('data') . '/plugged')
    Plug 'ncm2/ncm2'
    Plug 'roxma/nvim-yarp'

    " enable ncm2 for all buffers
    autocmd BufEnter * call ncm2#enable_for_buffer()

    " IMPORTANT: :help Ncm2PopupOpen for more information
    set completeopt=noinsert,menuone,noselect

    " NOTE: you need to install completion sources to get completions. Check
    " our wiki page for a list of sources: https://github.com/ncm2/ncm2/wiki
    Plug 'ncm2/ncm2-bufword'
    Plug 'ncm2/ncm2-path'
   Plug 'ncm2/ncm2-racer'
call plug#end()

neovim :messages output when the error occurs

Log files if you think the issue is a bug

2019-12-06 10:52:14,845 [ERROR @ base_events.py:default_exception_handler:1285] 1092 - Exception in callback _ProactorBaseWritePipeTransport._loop_writing(<_OverlappedF...ed result=133>)
handle: <Handle _ProactorBaseWritePipeTransport._loop_writing(<_OverlappedF...ed result=133>)>
Traceback (most recent call last):
  File "C:\Applications\Python\lib-python\3\asyncio\events.py", line 145, in _run
    self._callback(*self._args)
  File "C:\Applications\Python\lib-python\3\asyncio\proactor_events.py", line 291, in _loop_writing
    self._write_fut = self._loop._proactor.send(self._sock, data)
  File "C:\Applications\Python\lib-python\3\asyncio\windows_events.py", line 457, in send
    ov.WriteFile(conn.fileno(), buf)
  File "C:\Applications\Python\lib_pypy\_overlapped.py", line 352, in WriteFile
    ret = _kernel32.WriteFile(self.handle, self.write_buffer, len(self.write_buffer), written, self.overlapped)
TypeError: initializer for ctype 'void *' must be a cdata pointer, not bytearray

Just installed ncm2 and can't make it work. Should it? Or do I have to do something else to make it?