My 3rd party excel plugin would not SSL/TLS connect to SSL webapp server host. The .NETframework\v4 or v5 registry setting worked for me after a reboot- did not test the logout and back in method (idk if reboot was required). If you're root CA is in your Trusted root certificate authorities, that method will not work (even after reboot). You can check workstation ciphers: ps>get-tlsCipherSuite to get a list. The ps>enable-tlsciphersuite is good if you know your missing one on your workstation and you know what you're missing to add.