Official file
The current Android build. Give the counter below a few seconds and the file releases by itself.
Keep this page open — the file starts automatically.
Call it two minutes from start to finish. Only the third step is out of the ordinary, and Android will not ask you again afterwards.
Seconds on 4G, a little patience on anything slower — an interrupted file is the usual cause of trouble later.
Pick Download anyway. That notice is aimed at the file format, not at this particular download.
Settings, then Apps, Special access, Install unknown apps, and hand it to whichever browser fetched the file.
Binding the number is the step people skip and later wish they had not.
Nothing happened
A manual button appears once the counter empties, so use that. Should the browser have intercepted the file, open its Downloads list and resume the held item from there.
"App not installed"
That package name is already taken on the device, generally by an earlier or tampered build. Strip it out first, check you have room, then run it again.
"Parse error"
You have a partial file. Discard it rather than reopening the same one, and pull a fresh copy once the signal is steady.
Play Protect stepped in
Android inspects anything sourced outside its store as a matter of routine. There is an override in the dialog. If using it does not sit right with you, stop there instead of searching for a way round.
I'm on an iPhone
This will not install, and nothing else will either. APK is an Android format, and no genuine iOS release of this app exists.
I'm on a laptop
That needs an Android emulator in between — the help page walks through it.