este es mi error

 fastify.io.of('/webusers').on('connect', (socket) => { ^ TypeError: Cannot read properties of undefined (reading 'of')

esto es lo que he definido. ¡Si alguien pudiera ayudar sería genial!

 const config = require('./config.json') const fastify = require('fastify')() const fastifySession = require('@fastify/session') const fastifyCookie = require('@fastify/cookie') const helmet = require('fastify-helmet') const mariadb = require('mariadb') const axios = require('axios') const querystring = require('querystring') const pool = mariadb.createPool({ host: config.database.host, user: config.database.user, password: config.database.password, database: config.database.db, connectionLimit: 10 })