By default all newly created apps are setup to embed in Shopify admin. You can follow these steps to make sure the setting is right for your app:

1. From your Partner dashboard, click Apps.
2. Click on the name of your app.
3. Click App Setup.
4. Click Manage under the Embedded app section.
5. Enable setting under the Embed your app in Shopify admin section. If you'd like to load your app inside Shopify admin, then the setting must be enabled.

Next steps

Access the Shopify App Bridge.