<PackageReference Include="Newtonsoft.Json" Version="13.0.3" />

ValidationEventHandler

public sealed delegate ValidationEventHandler : MulticastDelegate

Represents the callback method that will handle JSON schema validation events and the ValidationEventArgs.

JSON Schema validation has been moved to its own package. See https://www.newtonsoft.com/jsonschema for more details.
using System; namespace Newtonsoft.Json.Schema { [Obsolete("JSON Schema validation has been moved to its own package. See https://www.newtonsoft.com/jsonschema for more details.")] public delegate void ValidationEventHandler (object sender, ValidationEventArgs e); }