Both admin and customer interfaces (online & in-store) of Rentle work in browser with every device that has been connected to Internet.
Admin url: my.rentle.shop
In-store kiosk: store.rentle.shop/your-slug
Online store: rentle.shop/your-slug
You will find your slug in the Shop settings under the Channels tab https://my.rentle.shop/shop/channels.
The most common reasons for that one of your interfaces is not loading are
Your device is not connected to Internet. Try loading another webpage.
The URL you are using is incorrect. Check the URL.
If your problem continues, you can always send message to email@example.com