I am using PayPalStandard plugin of NopCommerce. When I placed the order & make payment with paypalstandard plugin after successful payment on paypal, it redirects to mercha
I had the same issue connecting to sandbox(nvp), everything was fine then yesterday the message "The request was aborted: Could not create SSL/TLS secure channel." appeared.
I believe PayPal updated their endpoints on 19/20 January 2016 to use TSL 1.2 and HTTP 1.1.
To resolve this, for .NET 4.5 and above add the following line of code before calling WebRequest.Create().
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;