TLS 1.2 not negotiated in .NET 4.7 without explicit ServicePointManager.SecurityProtocol call

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I had the same issue (Windows 10 and SSL3 / TLS only… not System Default) with a legacy app targeting 4.7.2. My issue was that during the upgrade process over the years we never added in the targetFramework to the system.web > httpRuntime element (Note: it did exist on system.web > compilation element). Before taking bigger steps, ensure your system.web looks something like the following:

<system.web>
    <compilation targetFramework="4.7.2"></compilation>
    <httpRuntime targetFramework="4.7.2" />
</system.web>

In the above example, swap 4.7.2 for whatever version of the framework you are currently using that is >= 4.7.

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