Does anyone have an example of how to get accessTokens for marketplace buyer-facing apps?

Hi,

I am building a marketplace where users on my marketplace can purchase products on shopify. Since the update to Shopify Cli 3, I have not been able to create storefront access tokens with shopify-app-express.

I am trying to use the shopify-app-express example below, but it keeps returning a 401 and 404. If anyone has a working example, I’d very much appreciate your feedback.

import { shopifyApp } from "@shopify/shopify-app-express";
const shopify = shopifyApp({

api: {

apiVersion: LATEST_API_VERSION,

restResources,

apiKey: 'my key',

apiSecretKey: 'my secret',

accessMode: 'offline',

scopes: ['read_products', 'etc.'],

hostName: 'ngrok link',

apiVersion: LATEST_API_VERSION,

isEmbeddedApp: true,

 },

auth: {

path: "/api/auth",

callbackPath: "/api/auth/callback",

 },

webhooks: {

path: "/api/webhooks",

 },

sessionStorage: new CustomSessionStorage()

});