A SiteSync test connection fails when using HTTPS to connect to the Destination server, even though it is using a domain name with a valid SSL certificate.
When trying to send data to another server, an error appears.
In Site synchronization, when clicking "Test connection" for the Target, it is unsuccessful.

SiteSync compatibility with TLS 1.3 varies depending on the Sitefinity version and hosting configuration:

• Sitefinity 15.3 (Azure App Service / Sitefinity Cloud)
  In a controlled test environment where TLS 1.3 was enabled on the destination server and traffic was served directly from *.azurewebsites.net (bypassing Cloudflare), the application operated as expected:
  
  • Frontend rendered correctly
  • Backend authentication is working as expected
  • SiteSync is working as expected
    
    
• Sitefinity 14.4 (Azure App Service)
  In a client scenario with TLS 1.3 enabled, SiteSync failed with the error, “Server https://<destination server> is not accessible.”

The exact cause is not known at this time.

None at this time, use the workaround below. 

Either disable TLS 1.3 or explicitly configure the application to use TLS 1.2 by specifying the protocol version in the ~/Global.asax.cs file:

protected void Application_Start(object sender, EventArgs e)
{
    ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
}

** This method offers limited flexibility, as Sitefinity may not function reliably across all environments. Additionally, reverting to a different TLS version would require rebuilding the project.

Progress Article(s):

1. Sitefinity TLS related issues