If the app cannot reach the game servers then you'll see some sort of connection error.
Please make sure that you are connected to the internet. If your connection seems okay, try restarting the app.
Sometimes connection loss can be caused by issues with your cache, firewalls, network load, etc.
Try switching to a different connection type, such as from Wi-Fi to cellular data or vice versa. If using a home network, try restarting your router.
If there are no immediate alternatives to your internet connection then try using a VPN service. You can browse and download free VPN apps on the Play Store or the App Store.
Regardless of the reason, connection errors are temporary and tend to self-resolve over time. If case that they don't, please open a ticket and we'll try to help.