.NET SDK System.AggregateException OAuth 2 access token is malformed ?

Message=Error in call to API function "users/get_current_account":
    The given OAuth 2 access token is malformed.

https://www.dropbox.com/developers/documentation/dotnet#tutorial

(a) installed Dropbox .NET SDK via NuGet

(b) registered Dropbox API app using the "App Console"

(c) copied this text from the .NET tutorial page mention above.

(d) replaced "YOUR ACCESS TOKEN" in the line below with the App key from step (b) above:

using (var dbx = new DropboxClient("YOUR ACCESS TOKEN"))

(e) the code compiles BUT crashes on the line after the using:

var full = await dbx.Users.GetCurrentAccountAsync();

The ERROR is:

Message=Error in call to API function
 "users/get_current_account":
 The given OAuth 2 access token is malformed."

The app key provided by the Dropbox App Console
is 15 alphanumeric characters with this form:

aannnaaaaaaaana

How can it be malformed when it was copied and pasted
from the middle of a page with an URL that even contained
the App key as part of the URL:

https://www.dropbox.com/developers/apps/info/aannnaaaaaaaana

The outer exception is:

System.AggregateException was unhandled
HResult=-2146233088