Change the default https port for access and block http access

I tested it today but couldn’t get it to work.
In fact it made things worse:

Test 1
Edited /etc/nginx/conf.d/gl.conf to
10 # listen 80;
11 # listen [::]:80;
12
13 listen 20999 ssl;
14 listen [::]:20999 ssl;
Result
→ unable to connect
192.168.119.1 refused to connect.
ERR_CONNECTION_REFUSED

Test 2
Edited /etc/nginx/conf.d/gl.conf to:
13 listen 20999 ssl;
14 listen [::]:20999 ssl;
Result
→ unable to connect
192.168.119.1 refused to connect.
ERR_CONNECTION_REFUSED

Test 3
Edited /etc/nginx/conf.d/gl.conf to the same listing port as uhttpd:
13 listen 21999 ssl;
14 listen [::]:21999 ssl;
Result
I can connect, but it goes straight to Luci - the GL interface is still not reachable.

Test 4 - very strange
I restored /etc/nginx/conf.d/gl.conf from backup copy
(made before I edited it)
Result
Same result!!
192.168.119.1 refused to connect.
ERR_CONNECTION_REFUSED

Same when trying to connect on the lan or wan side.
I checked the firewall rules - there is nothing changed there.
I can connect to the Luci interface - no problems, and via ssh.

The only explanation I can think of is that nginx now refuses to start.
I did a htop to see running processes,
and I can see uhttpd but not nginx.