SSL Problems in C#

[TheForestGump]

DeepLHelper.cs.txt
frm_DeepL.cs.txt

Hello ... I've been trying for hours to do a test translation via the API with C#. Both with .NET 4.8, as well as with .NET Core 6.0. This via HTTPClient, WebClient, NugetPackage and HTTPWebRequest. I always get the error message that no protected SSL channel has been opened. I have installed all certificate handlers. My code works against other SSL APIs ... only against the DeepL-API I do not get a call ... Can someone please help?

[ntduong1998vn]

It seems that my response is a bit late, but I believe others might encounter the same issue.
After investigating, I found that the root cause could be that your framework version is outdated, so its default to older protocols ( (TLS 1.0/1.1) . Meanwhile, the DeepL library expects the protocol to be TLS 1.2, so you need to configure the SecurityProtocol accordingly.

ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls13;

I added the line of code below before calling the DeepL API, and it worked.
Hopefully, this will help you and others who run into the same problem.