Clightning with BTCpay server failed
I found it. The port 9735 is not open to the public. 

Go to google cloud console

Home -&gt; VPC network -&gt; Firewall rules

+ Create firewall rule:

Name      Type    Targets   Filters          Protocols / ports  Action  Priority    Network
lightning Ingress Apply to all  IP ranges: 0.0.0.0/0 tcp:9735       Allow   1000        default