To support the Hybrid Connections it's configured with, HCM requires: TCP access to Azure over port 443.
To fetch more details about the issue and logs.
Troubleshoot Hybrid Connection Issues - Windows/Linux
Just to highlight, in App Service, the tcpping command-line tool can be invoked from the Advanced Tools (Kudu) console. This tool can tell you if you have access to a TCP endpoint, but it doesn't tell you if you have access to a Hybrid Connection endpoint. When you use the tool in the console against a Hybrid Connection endpoint, you're only confirming that it uses a host:port combination.
Azure App Service Hybrid Connections | Troubleshooting
Troubleshooting Hybrid Connections with Logging
--You may always leverage App Service diagnostics from Azure Portal> Navigate to your App Service app in the Azure Portal.
In the left navigation, click on Diagnose and solve problems
- Review and run – Network troubleshooter and ““Configuration and Management” (IP address configuration).