I have a .NET Framework 4.8 application that is using Flurl to initiate requests against an endpoint. But whenever we are trying to access the endpoint, TLS 1.0 is being used. When I print out ServicePointManager's SecurityProtocol, it will print out Ssl3, Tls. Our code does not override this, so this has to come from either the system or an external dependency and as far as I'm aware the value it defaults to seems like it's .NET Framework 4.5.

So I created a quick test application that just uses Flurl to go against the same service and this time it used TLS 1.2 (which would be sufficient in my original use case), but based on my understanding, it should have been able to negotiate with TLS 1.3 (the service supports it).

The original code is working on every other box, except this one. I've already checked the registry entries to see if higher versions of TLS are disabled, but they are not. At this point I'm not sure how to proceed as trying all of the external dependencies individually to see if they are causing the issue is not really feasible (+ would not explain why it would work on other boxes).

Any help is really appreciated, thank you in advance.