https://www.gamespot.com/articles/fortnites-android-beta-expanding-to-more-phones-he/1100-6461129/

Epic's popular battle royale game, Fortnite, made its highly anticipated debut on Android devices last week--but only for some users. Thanks to a deal with Samsung, the title was initially only available on certain Samsung phones. That exclusivity period has now ended, and Epic has begun inviting other users to try out the Android version of Fortnite ahead of its full release on the platform.

Despite rolling out for more devices, the Android version of Fortnite still isn't widely available to download; rather, if you're hoping to play the battle royale game on your Android phone, you'll first need to sign up for an invitation on the Fortnite Android website. These are gradually being sent out via email to more and more players, so you may not receive an invitation right away if you've only recently signed up.