using LukeHagar.PlexAPI.SDK;
using LukeHagar.PlexAPI.SDK.Models.Components;

var sdk = new PlexAPI(accessToken: "<YOUR_API_KEY_HERE>");

var res = await sdk.Media.UpdatePlayProgressAsync(
    key: "<key>",
    time: 90000D,
    state: "played"
);

// handle response

This response does not have an example.