"There’s no page at this address" error on Shopify Embedded App installation

This happened with our sales channel too and the reason was that shopify’s "APP_UNINSTALLED" webhook does not get called properly or some delay happens so the session_token does not get cleared (which you might be doing in that webhook handler). And because of using an expired token, you end up on that page.

How we fixed it was we retrieve the saved session from session storage and use it to hit any shopify admin api and if that fails with a 401 or 403 error then we assume that it is an expired token and clear it.

Something like this:

app.get("/", async (req, res) => {
  if (typeof req.query.shop !== "string") {
    res.status(500);
    return res.send("No shop provided");
  }

  const shop = Shopify.Utils.sanitizeShop(req.query.shop) || "";
  const sessions = await Shopify.Context.SESSION_STORAGE.findSessionsByShop(shop);

  const { AccessScope } = await import(
  `@shopify/shopify-api/dist/rest-resources/${Shopify.Context.API_VERSION}/index.js`
  );

  const scope = await AccessScope.all({
    session: sessions[0],
  }).catch(async (err) => {
    // We check for the error status code and clear our storage
    if (err.response?.code === 401 || err.response?.code === 403) {
      sessions.forEach((session) => redisClient.del(session.id));
      await AppInstallations.delete(shop);
    }
  });
  const appInstalled = await AppInstallations.includes(shop);

  if (!appInstalled) {
    return redirectToAuth(req, res, app);
  }

  if (Shopify.Context.IS_EMBEDDED_APP && req.query.embedded !== "1") {
    const embeddedUrl = Shopify.Utils.getEmbeddedAppUrl(req);

    return res.redirect(embeddedUrl + req.path);
  }

  return handle(req, res);
)};

const AppInstallations = {
  includes: async function (shopDomain: string) {
    if (Shopify.Context.SESSION_STORAGE.findSessionsByShop) {
      const shopSessions =
        await Shopify.Context.SESSION_STORAGE.findSessionsByShop(shopDomain);
      if (shopSessions.length > 0) {
        for (const session of shopSessions) {
          if (session.accessToken) return true;
        }
      }
    }
    return false;
  },

  delete: async function (shopDomain: string) {
    if (Shopify.Context.SESSION_STORAGE.findSessionsByShop) {
      const shopSessions =
        await Shopify.Context.SESSION_STORAGE.findSessionsByShop(shopDomain);
      if (shopSessions.length > 0) {
        if (Shopify.Context.SESSION_STORAGE.deleteSessions) {
          await Shopify.Context.SESSION_STORAGE.deleteSessions(
            shopSessions.map((session) => session.id)
          );
        }
      }
    }
  },
};