The TypeScript definitions have

export interface NavigationEventPayload {
 type: EventType;
 action: NavigationAction;
 state: NavigationState;
 lastState: NavigationState | null | undefined;
}

So I think it should be NavigationState.t / option(NavigationState.t).

Actually, if it can really be null and not just undefined, we need Js.Nullable.t(NavigationState.t).

Thank you for bearing with me while I am starting with ReasonML.

I have the following error:

src/Navigation.re 33:3-21
 
 31 ┆ navigationEventPayload => unit
 32 ┆ ) =>
 33 ┆ EventSubscription.t =
 34 ┆ "addListener";
 35 ┆ 
 
 The module or file EventSubscription can't be found.

but reason-react-native seems to be in bsconfig.json nonetheless any idea how to make it visible?

open ReactNative; fixed it!