Fortnite Beta for Android is not available on the Google Play. You need to sign up for beta on the official Epic Games website https://www.epicgames.com/fortnite/en-US/mobile/android/sign-up

ANDROID BETA INITIALLY WILL WORK ON THE FOLLOWING DEVICES:

• Samsung Galaxy: S7 / S7 Edge, S8 / S8+, S9 / S9+, Note 8, Note 9, Tab S3, Tab S4
• Google: Pixel / Pixel XL, Pixel 2 / Pixel 2 XL,
• Asus: ROG Phone, Zenfone 4 Pro, 5Z, V Essential: PH-1
• Huawei: Honor 10, Honor Play, Mate 10 / Pro, Mate RS, Nova 3, P20 / Pro, V10
• LG: G5, G6, G7 ThinQ, V20, V30 / V30+
• Nokia: 8
• OnePlus: 5 / 5T, 6
• Razer: Phone
• Xiaomi: Blackshark, Mi 5 / 5S / 5S Plus, 6 / 6 Plus, Mi 8 / 8 Explorer / 8SE, Mi Mix, Mi Mix 2, Mi Mix 2S, Mi Note 2
• ZTE: Axon 7 / 7s, Axon M, Nubia / Z17 / Z17s, Nubia Z11