How to package a coc extension for vim

I have packaged some vim plugins on my own before and they seem to work unless they are a coc-extensions. For example, I want to install the elixir extension:

  coc-elixir = pkgs.vimUtils.buildVimPluginFrom2Nix {
    name = "coc-elixir";
    src = pkgs.fetchFromGitHub {
      owner = "elixir-lsp";
      repo = "coc-elixir";
      rev = "a48b9c8fd8651fc3886b16f5c2fc367d91f4cffc";
      sha256 = "sha256-xHCX3KWtA2+YrGRgua+vdI+8/yEJQjnZS0u82eHhuqw=";

I don’t get any errors but the extension does not get loaded into vim.
Does anyone know the correct way to package coc extensions?

I dont use coc but home-manager has some special-handling for coc so you might want to look int it.
Certainly it needs a node environment with all the correct libraries. Maybe coc.nvim has some :checkhealth that could point you into the right direction ?