OpenAI_API Assembly Not Found

I’m a C# developer new to OpenAPI. I just installed through NuGet package OpenAI (the official .NET library for the OpenAI service API).

The first step is to use the newly installed package. From an example in C#, the following is the statement to use the assembly:

using OpenAI_API;

But, OpenAI_API is NOT found in the installed package.

Any help is appreciated.