provenance/coffin_promise/40 matches the site

public static Activity Promise_Activity()
{
    var activity = new Activity()
        .WithContext()
        .WithId("https://linked.art/example/provenance/coffin_promise/40")
        .WithLabel("Promised Gift of Painting")
        .WithClassifiedAs(Aat.ProvenanceActivity);

    activity.Part = [
        new Activity()
            .WithLabel("Promise of Gift")
            .WithClassifiedAs(Aat.PromiseActivity)
    ];

    return activity;
}

var activity = new Activity
{
    Context = ["https://linked.art/ns/v1/linked-art.json"],
    Id = "https://linked.art/example/provenance/coffin_promise/40",
    Label = "Promised Gift of Painting",
    ClassifiedAs = [Aat.ProvenanceActivity],
    Part =
    [
        new Activity
        {
            Label = "Promise of Gift",
            ClassifiedAs = [Aat.PromiseActivity],
        },
    ],
};

Generated from the object the example builds: every property that is set, as object initialisers, with the vocabulary constants where a term is in the registry. The fluent helpers are a convenience, not a requirement; this form and the one as written produce the same JSON.