We have the same issue, we fixed this by modified the library. Most of our project which uses Podio Sync library. Podio Sync library belongs to Dotnet framework 4.0, so we added a line of code to set default security protocol.
ServicePointManager.SecurityProtocol = (SecurityProtocolType)768 | (SecurityProtocolType)3072;
The changes are done in Podio.cs file line 76
private T Request<T>(RequestMethod requestMethod, string url, dynamic requestData, dynamic options = null)
where T : new()
{
Dictionary<string, string> requestHeaders = new Dictionary<string, string>();
changed to
private T Request<T>(RequestMethod requestMethod, string url, dynamic requestData, dynamic options = null)
where T : new()
{
ServicePointManager.SecurityProtocol = (SecurityProtocolType)768 | (SecurityProtocolType)3072;
Dictionary<string, string> requestHeaders = new Dictionary<string, string>();
Hope this will help..
The solution for the SecurityProtocol issue can be found C# HttpWebRequest The underlying connection was closed: An unexpected error occurred on a send