The underlying connection was closed

The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.

solución:

ServicePointManager.ServerCertificateValidationCallback = AddressOf ValidateRemoteCertificate

 'Public Shared Function ValidateRemoteCertificate(ByVal sender As Object, ByVal certificate As X509Certificate, ByVal chain As X509Chain, ByVal sslPolicyErrors As Net.Security.SslPolicyErrors) As Boolean
    '    Return True
    'End Function


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