GPT-35 No such host is known

Recently I started testing the GPT 3.5 API in C#. First, I created an exe program and tested it, and when it worked normally, I tried to add it to a web service.

However, because it is not .NET 6.0 version, I could not create the service myself. I chose to run the exe program within the service, and confirmed that it worked normally locally.

So I immediately reflected it on the server, and the following message appeared.

“No known hosts. (api . openai . com : 443)”

There are no special issues with the firewall (including inbound and outbound), but an error like this occurs and I cannot use it, so I would like to ask for advice on this.

Firewall check OK

[local]
Run directly as program > OK
Run exe via service > OK

[server]
Run directly as program > OK
Running exe via service > NOPE

(cf. Development was carried out using the Betalgo.OpenAI.GPT3 package, and the program has sufficient IIS permissions.)