Suddenly unable to connect to the host

[memo_link]

I called the Rest APIs by the C# library（Coretweet）.
But it didn’t work from the day before yesterday.
The error code is 10054.
The error message is “An existing connection was forcibly closed by the remote host”.
How can I solve this problem?

[memo_link]

I’ve solved the problem with this code.
System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;