There are a few solutions you can try if the game is not loading:
1. Ensure you have a Wifi and/or data connection.
2. Try turning Mobile Data / Wifi OFF and then ON again.
3. Try restarting the game completely (full shutdown and restart).
4. Try restarting your device (reboot after 30 seconds).
5. Check if there are any firewalls applied to your Wifi that may be blocking the game's access to use the network properly.
6. If you are currently using a WiFi connection, turn WiFi off and attempt to use Mobile Data instead.
7. Reset the device network:
iOS - Go to Settings > Choose General > Reset > click Reset Network Settings > Turn off WiFi network > Turn off iPhone > reboot iPhone and WiFi network.