can you transfer a game from iphone to android

You cannot transfer a game app from an iPhone to an Android phone, or vice versa. The phones use different operating systems, and games written for one operating system are not compatible with the other.

As to whether an app developer who has written both iOS and Android versions of a game would let you switch without paying again, I don't know. There are some "subscription" products (like Microsoft 365 or Adobe ones) where paying a "subscription" fee might offer you access to desktop and mobile apps on multiple platforms, but unless a developer explicitly says that your purchase gets you access to apps for multiple platforms, it is safer to assume that you are talking about purchasing the app separately for each platform.