“The thumbprint (cert hash) of the certificate used for Secure Socket Tunneling Protocol (SSTP) is different than the certificate bound to the Web listener (HTTP.sys). Configure SSTP to use the default certificate or the certificate bound to SSL. You can configure web server applications to use the same certificate used by SSTP.”
IIS Binding
Most commonly this error can occur if an administrator mistakenly binds a TLS certificate directly in IIS. To resolve this problem, open the IIS management console (inetmgr.exe), navigate to the Default Web Site and click Bindings in the Actions section. Highlight the HTTPS binding and click Remove. Once complete, open an elevated command window and run the iisreset.exe command.
Netsh
In some instances, the administrator may find no certificate bindings in the IIS management console. However, a certificate binding may still be present. To confirm, open an elevated command window and run the following command.
netsh.exe http show sslcert
Remove existing certificate binding by running the following commands.
netsh.exe http delete sslcert ipport=0.0.0.0:443
netsh.exe http delete sslcert ipport=[::]:443
SSTP Configuration
When configuring SSTP in RRAS for Always On VPN, certificate assignment should always be performed using the Routing and Remote Access management console (rrasmgmt.msc). No changes are required to be made in the IIS management console for SSTP.
Additional Information
Windows 10 Always On VPN SSL Certificate Requirements for SSTP
Windows 10 Always On VPN SSTP Load Balancing with Citrix NetScaler ADC Load Balancer
Windows 10 Always On VPN SSTP Load Balancing with Kemp LoadMaster Load Balancer
Windows 10 Always On VPN SSTP Load Balancing with F5 BIG-IP Load Balancer