It's not that easy. Im having the same problem. And my phone tells me i don't have what i need to process it and it makes me download another app... like unRAR and I downloaded it and tried everything but still no luck... witch is a shame because I would love to support the developer and game but im not doing it if i can't download and play
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Maybe the Zarchiver app could would better for you. You will need an app to extract rar first. Then install the apk. There should be a lucky.paradox folder in documents after that. And inside it is a game folder. That is where the archive.rpa file goes. Then transfer your saves and it should load. If there isn’t a save folder then start the game and a new save then it should automatically be created. You can also check this video out on how to do that:
Also a step by step guide here:
https://www.patreon.com/posts/android-master-82619463
Hopefully that helps and solves it