I have just set up a new instance on my Ubuntu server and I see the following error pop up continuously

the config.json is set up to point to the correct url
{
"url": "http://forum..co.uk",
"port": "4567",
"use_port": false,
"secret": "",
"database": "mongo",
"mongo": {
"host": "127.0.0.1",
"port": "27017",
"username": "forum",
"password": "********************",
"database": "forumdb",
"uri": ""
}
}
My Nginx config is also set up correctly
{
listen 80;
ssl_certificate /etc/ssl/certs/forumcert.pem;
ssl_certificate_key /etc/ssl/certs/bmansi.key;
server_name forum.*****.co.uk;
location / {
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_set_header Host $http_host;
proxy_set_header X-NginX-Proxy true;
proxy_pass http://127.0.0.1:4567;
proxy_redirect off;
# Socket.IO Support
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
auth_basic "Restricted Content";
auth_basic_user_file /etc/nginx/.htpasswd;
}
}
I've restarted, rebooted, tried with SSL without SSL and so far have been completely unable to remove the popup loop when browsing to my site in Chrome or Edge.
Does anyone have any suggestions?