Why can't find namespace name 'NJsonSchema'?

[DCores]

hello

there is a problem with Unity3DTiles

when i import Unity3DTiles into project,there is a errer:

Assets\Plugins\Unity3DTiles\SchemaGen\Generate\Program.cs(2,7): error CS0246: The type or namespace name 'NJsonSchema' could not be found (are you missing a using directive or an assembly reference?)

Why can't find namespace name 'NJsonSchema'?

is 'NJsonSchema' in \Unity3DTiles\Assets\JsonDotNet\Assemblies\Standalone\Newtonsoft.Json.dll ?

the error is cause by Program.cs Line 1 and Line 2:
using NJsonSchema;
using NJsonSchema.CodeGeneration.CSharp;

my unity version is 2018.4.35f1

thank you and hope for your reply :)