[Rey_a]

Not sure what you are asking here.

As far as I know, crossplay in the world of gaming means that different people can play online games together even though they are using different platforms to play those games from ...

So if you are asking if a version of MobileSheets on Android can work together (synchronise with, exchange backups with ....) with a version on iOs, then the the answer is yes.

If you are asking if you need to buy again to use MS on a different platform, then the answer is also yes.
If you bought your Android License through the Google Play Store, you can use that license to install MS on several Android devices, provided you use the same user account. You cannot use it however to install MobileSheets on iOS or on Windows. For that you need to buy again in the corresponding app store.