The ‘local internal’ server runs on port 8000.
frappe@ubuntu1804lts:~/frappe-bench$ sudo netstat -tlnp
[sudo] password for frappe:
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 127.0.0.1:11000 0.0.0.0:* LISTEN 1818/redis-server 1
tcp 0 0 0.0.0.0:25 0.0.0.0:* LISTEN 1468/master
tcp 0 0 0.0.0.0:8000 0.0.0.0:* LISTEN 1823/python
tcp 0 0 127.0.0.1:12000 0.0.0.0:* LISTEN 1807/redis-server 1
tcp 0 0 127.0.0.1:13000 0.0.0.0:* LISTEN 1803/redis-server 1
tcp 0 0 0.0.0.0:3306 0.0.0.0:* LISTEN 1348/mysqld
tcp 0 0 127.0.0.1:6379 0.0.0.0:* LISTEN 860/redis-server 12
tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 904/nginx: master p
tcp 0 0 127.0.0.1:53 0.0.0.0:* LISTEN 965/dnsmasq
tcp 0 0 192.168.0.206:53 0.0.0.0:* LISTEN 965/dnsmasq
tcp 0 0 127.0.0.53:53 0.0.0.0:* LISTEN 779/systemd-resolve
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 916/sshd
tcp6 0 0 :::25 :::* LISTEN 1468/master
tcp6 0 0 :::9000 :::* LISTEN 1825/node
tcp6 0 0 ::1:6379 :::* LISTEN 860/redis-server 12
tcp6 0 0 ::1:53 :::* LISTEN 965/dnsmasq
tcp6 0 0 fe80::5054:ff:fef0:f:53 :::* LISTEN 965/dnsmasq
tcp6 0 0 :::22 :::* LISTEN 916/sshd
A search turns up pointers to try like this: