Paypal RESTful API ASP.NET C#

I am trying to implement the Paypal RESTful API to be able to receive payments on my website. At this stage I have been able to make the sample code work.

More specifically I have created a brand new application in VS2013 and copy pasted the following files from the sample API's: PaymentWithCreditCard.aspx, Response.aspx and Configuration.cs. The result is that I can successfully post payments to the sandbox and get a response of an approved payment. So far so good.

Problem N1 - retrieving an access token

I have replaced in the configuration class file the sample standard access token:

        private static string GetAccessToken()
        {
OAuthTokenCredential("EBWKjlELKMYqRNQ6sYvFo64FtaRLRR5BdHEESmha49TM", "EO422dn3gQLgDbuwqTjzrFgFtaRLRR5BdHEESmha49TM", GetConfig()).GetAccessToken();
            return accessToken;
        }

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with the following:

        private static string GetAccessToken()
        {
            var clientId = System.Configuration.ConfigurationManager.AppSettings["clientId"];
            var secretToken = System.Configuration.ConfigurationManager.AppSettings["secretToken"];
            var config = new Dictionary<string, string> { { "mode", "sandbox" } };

            OAuthTokenCredential tokenCredential = new OAuthTokenCredential(clientId, secretToken, config);
            string accessToken = tokenCredential.GetAccessToken();
            return accessToken;
        }

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and i have also added in web.config the following:

  <configSections>
    <section name="paypal" type="PayPal.Manager.SDKConfigHandler, PayPalCoreSDK"/>
  </configSections>
  <paypal>
    <accounts>
      <account apiUsername="" apiPassword="" applicationId="" apiSignature="" />
    </accounts>
    <settings>
      <add name="mode" value="sandbox" />
    </settings>
  </paypal>
  <system.web>
    <compilation debug="true" targetFramework="4.5" />
    <httpRuntime targetFramework="4.5" />
  </system.web>
  <appSettings>
    <add key="clientId" value="***********" />
    <add key="secretToken" value="***********" />
  </appSettings>
</configuration>

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however I get a

Exception in HttpConnection Execute: Invalid HTTP response The remote server returned an error: (401) Unauthorized.

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The sample files are from
https://github.com/paypal/rest-api-sdk-dotnet/tree/master/Samples/RestApiSample