Just copying/pasting from a post I made elsewhere, but here it is in case others are wondering (or you still are)
There is an in-game currency (crowns) that you can purchase with real money. You also get quite a few of these through doing normal quests and missions. It is NOT pay to win. Having a stockpile of crowns won't give you a significant advantage at all. The crowns allow you to halve building time on buildings (not really that useful at all) and purchase a few special units. The special units are great but take up significantly more unit slots so their usefulness is debatable. The one thing they are used for is purchasing unit upgrades. There are a finite number of upgrades and through the course of playing normally, you will earn enough to buy all the upgrades.