Hey Konju!
Sorry you're experiencing issues getting the game to unpack.
There's a few things you can try doing: Making sure the Launcher has the necessary permissions (allow all). If this is already in place, you can disable and re-enable to retry. Deleting and reinstalling the launcher can help too.
When downloading the RPA file, make sure its not paused or interrupted as it can cause the game to corrupt on installation/unpacking.
Also, make sure the RPA is put inside the actual "game" folder itself. Like shown below. Please let me know if these help!