It still in its development stage, but you can already try it out in your own games. GDevelop has a community extension which makes in-app purchases possible.
Incorporate this mechanic as early in the game development process as possible. So, if you're going for an in-app purchase model, be sure to focus on items that do not affect the balancing of your game. Nobody wants to feel like they're playing a game against people who have just paid to win. The trend at the moment is to exclude upgrades which affect the balancing of the game, and focus on aesthetic items or timers instead.
