wss connection to node ws server via nginx, ERR_CERT_AUTHORITY_INVALID - node.js

Question

I have a websocket server running behind nginx.
Connecting via http works ok (ws://mywebsite.com) with following nginx config:
http {
server {
listen 80 default_server;
listen [::]:80 default_server;
server_name _;
root /usr/share/nginx/html;
location /myWebSocket {
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
proxy_pass http://localhost:5000;
}
}
}
I'd like to connect to this via https (wss://mywebsite.com) and have tried this:
http {
server {
listen 443 ssl http2 ;
listen [::]:443 ssl http2 ;
server_name mywebsite.com; # managed by Certbot
root /usr/share/nginx/html;
ssl_certificate /etc/mycert.pem;
ssl_certificate_key /etc/mykey.pem;
ssl_session_cache shared:SSL:1m;
ssl_session_timeout 10m;
ssl_ciphers PROFILE=SYSTEM;
ssl_prefer_server_ciphers on;
location /myWebSocket {
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
proxy_pass http://localhost:5000;
}
}
}
However, I get a ERR_CERT_AUTHORITY_INVALID on the browser side (e.g. with wss://myWebsite/myWebSocket).
My understanding is that WSS is a connection to a standard websocket via https, is this correct?
Is my approach above correct?
Is there something obvious I'm doing wrong?
To confirm the cert was installed with certbot, and the e.g. https://example.com works.
Note also, there is another server block listening on 443, this does not define the /myWebSocket location (I think it is the nginx default ssl block that is superceded by certbot block).
Edit: note removing that first ssl server block results in the browser side websocket connection error message changing to ERR_CERT_COMMON_NAME_INVALID.
Another Edit: I was connecting using the server's IP address not the DNS name - that removed the error. :-)