If the issue happens when you’re playing on a Mobile Data connection, try to see if it still happens while using a Wi-Fi connection.
If you are already using a Wi-Fi connection, try restarting your device and your Wi-Fi router as well.
Sometimes, it might be a temporary server failure. In such cases, we are able to spot the problem quickly and alert the responsible teams. So it makes sense for you to wait for an hour or so and try to connect later.