Package added with nuget, but can't using

I added a nuget package to a C#asp.core net 3 application:

dotnet add package NQuantLib64 --version 1.0.9

I can see the package in the project:

idf@ubvm:~/Documents/Projects/OptionsAPI$ grep -i Quantlib OptionsAPI.csproj 
    <PackageReference Include="NQuantLib64" Version="1.0.9" />
idf@ubvm:~/Documents/Projects/OptionsAPI$

But when I try to use it, it says it can't find it?

using QuantLib;

Unnecessary using directive. [OptionsAPI]csharp(CS8019)
The type or namespace name 'QuantLib' could not be found (are you missing a using directive or an assembly reference?) [OptionsAPI, OptionsAPI]csharp(CS0246)