As Ready does not allow you to add ads within their system, you have to export your project into Unity to do so.
I’m currently working on a mobile game right now that’s being built off a pc version of my game and what I know so far is that you need to make sure you have services turned on in Unity.
If you wish to learn how to program ads into your game, here is a tutorial I have been watching:
Also, when you publish to iOS and Android, don’t forget to mark if your game has ads or not because they will check for that.
There are also many different services that allow you to have ads. The most common are Unity Ads which are very easy to implement, and AdMob which is harder to implement but allows more leverage. I’ve heard very negative things about unity ads sometimes, but sometimes it’ll work for some people. Not everyone is lucky with them however.