Unable to establish trust relationship for SSL / TLS secure channel

[marcodonza]

Hi,
when, after authentication, I go to read the orders, in the Execute function I always get the error indicated below.
What does it mean ?

I set the string at the start of the project

System.Net.ServicePointManager.SecurityProtocol = System.Net.SecurityProtocolType.Tls12;

protected async Task<MagentoApiResponse> Execute(IRestRequest request, bool isSecondTry = false) where T : new()
{
Client.FollowRedirects = request.Method != Method.POST;
//var response = await Client.ExecuteTaskAsync(request);
var response = await Client.ExecuteAsync(request);
if (response.ContentType.ToUpperInvariant().Contains("APPLICATION/JSON"))

return this error, and response.ContentType is null

Underlying connection closed: Unable to establish trust relationship for SSL / TLS secure channel.

Please help me!

Thanks
Marco