Error when hooking to nvim-lspconfig

Language Server Protocol (LSP)
1

I am writing a plugin that uses ltex-ls to check the grammar while writing LaTeX or Markdown documents.

In it, I am hooking to nvim-lspconfig, so that the end user can use require("lspconfig").grammar_guard.setup{}.

I have done it like this

	local configs = require("lspconfig/configs")
	local util = require("lspconfig/util")

	local bin_path = require("grammar-guard.vars").bin_path

	configs.grammar_guard = {
		default_config = {
			cmd = { bin_path },
			filetypes = { "tex", "bib", "markdown" },
			root_dir = function(filename)
				return util.path.dirname(filename)
			end,
			settings = {
				ltex = {
					checkFrequency = "edit",
				},
			},
		},
		docs = {
			package_json = "https://raw.githubusercontent.com/valentjn/vscode-ltex/develop/package.json",
			description = [[
                https://github.com/valentjn/ltex-ls

                LTeX Language Server: LSP language server for LanguageTool 🔍✔️ with support for LaTeX 🎓, Markdown 📝, and others

                To install, download the latest [release](https://github.com/valentjn/ltex-ls/releases) and ensure `ltex-ls` is on your path.

                ]],

			default_config = {
				root_dir = "vim's starting directory",
			},
		},
	}

This snippet runs without errors, but when I call:

require("lspconfig").grammar_guard.setup{}

It produces an error which states that the setup function is nil.
What have I missed?