One2One is distributed as a direct APK download, not through Google Play. Android blocks installs from outside the Play Store by default, so you'll need to allow it once — takes under a minute.
On your Android phone, open the download link from the home page in Chrome. Choose the ARM64 build unless your device is very old or unusual — it covers virtually all phones from 2018 onward.
When you tap the downloaded file, Android will show a prompt saying installs are blocked. Tap Settings on that prompt, then enable Allow from this source for Chrome (or whichever app you downloaded with). This is a one-time setting per app.
Go back and tap the APK file again, then tap Install. Android may show a Play Protect warning since the app isn't from the Play Store — tap Install anyway to proceed.
Launch One2One from your app drawer, sign in, and you're ready to place your first bet.