When something is wrong

The usual problems, and what to do about them.

The keyboard does not open when I tap a field: Update to the newest build: older ones had a bug where the first tap opened the keyboard and closed it again. If it still happens, turn on Show FPS in Game Settings and send us the line it prints at the top-left while a field is selected.
The download stops, or crawls: It carries on where it stopped, so open the app again and let it run. A phone that sleeps pauses it; keep the screen on for the first download.
It says there is not enough space: The game data needs several gigabytes free while it unpacks. Clear some room and start it again; nothing already downloaded is lost.
It says the app is too old: The server has set a floor below which an app may not play. Install the build offered on the update screen, or from your server's download page.
Android will not install the file: Android asks once whether to allow installing apps from wherever you downloaded it. Allow it for that app, then open the file again.
It cannot reach the server: Check that the PC client can, and that the server is up; the app connects to exactly the same addresses. Some networks block them, and mobile data often works where a hotspot does not.
Something looks wrong, or a file seems damaged: Settings has Repair game files: it checks every file and downloads only the damaged ones.
It runs slowly: Lower the quality and the frame limit in Game Settings, and turn off skill effects. Older phones are happier with fewer things drawn at once.

Still stuck? Tell us what happened.