For resources with Attrs that are complex types, there should be a way to pass a specific contract resolver for formatting. Without this support, you can end up with mixed casing results:

class MyEntity : Identifiable { [Attr("my-complex-type")] MyComplexType MyComplexType { get; set; } }

{ "data": [{ "type": "my-entity", "id": "1", "attributes": { "my-complex-type": { "Key1": "Value1" } } }] }