We develop our first app and use Shopify gem. It works fine and all functionality (including installation flow) is working well.
We've sent the app for a review and received an answer with following comment from their QA: After installing the app from the Shopify App store, the app is redirecting to the website where the app is hosted. When accessing the app from a shop's app dashboard, the app is redirecting to the embedded version. This occurs when an initial OAuth request redirect fails to escape the iframe. Please refer to our embedded app OAuth documentation (https://help.shopify.com/en/api/embedded-apps/embedded-app-sdk/oauth) for further information.
Has anybody faced with this problem? Shopify QA doesn't answer our e-mails and we couldn't find any useful requirements or information on shopify forums.