Method not found: 'System.Net.Http.HttpRequestMessage System.Web.Http.Controllers.HttpActionContext.get_Request()'

Are you referencing a .NET Standard Library by any chance. I ran into this problem and solved it with a Binding Redirect:

  <dependentAssembly>
    <assemblyIdentity name="System.Net.Http" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
    <bindingRedirect oldVersion="0.0.0.0-4.0.0.0" newVersion="4.2.0.0" />
  </dependentAssembly>