Use custom action in wix bootstrapper | Wixsharp

Question

I have a simple bootstrapper installer in wixsharp and I'd like to use a custom action like that:

 bootstrapper.AddWixFragment("CustomActions",
            new ManagedAction(CustomAction.MyAction, Return.check, When.Before, Step.InstallInitialize, Condition.NOT_BeingRemoved, Sequence.InstallUISequence));

But I get error cannot convert type ManagedAction to type XElement

from this link, it seems I can use custom action in WIX

How can i use custom action in wix bootstrapper in wixsharp?

Thx