I’m running nextcloud AIO v5.1.0, hosted on a cloud service provider, Ubuntu 22.04.2 LTS. NextCloud Office had previously been working but is no longer working.

The output of your Nextcloud log in Admin > Logging :

PASTE HERE
Formatted 
[richdocuments] Error: GuzzleHttp\Exception\ConnectException: cURL error 7: Failed to connect to "FQDN of Nextcloud server.com" port 443 after 1 ms: Connection refused (see https://curl.haxx.se/libcurl/c/libcurl-errors.html) for https://FQDN of Nextcloud server.comhosting/capabilities at <<closure>>
"remoteAddr":"my home isp address","user":"XXX","app":"richdocuments","method":"GET","url":"/apps/logreader/poll?lastReqId=uitqMzdjzRvj42WsUkvA","message":"Failed to fetch the Collabora capabilities endpoint: cURL error 7: Failed to connect to "FQDN of Nextcloud server.com" port 443 after 1 ms: Connection refused (see https://curl.haxx.se/libcurl/c/libcurl-errors.html) for https://"FQDN of Nextcloud server.com"/hosting/capabilities","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:109.0) Gecko/20100101 Firefox/113.0","version":"25.0.6.1","exception":{"Exception":"GuzzleHttp\\Exception\\ConnectException","Message":"cURL error 7: Failed to connect to "FQDN of Nextcloud server.com" port 443 after 1 ms: Connection refused (see https://curl.haxx.se/libcurl/c/libcurl-errors.html) for https://"FQDN of Nextcloud server.com"/hosting/capabilities","Code":0,"Trace":[{"file":"/var/www/html/3rdparty/guzzlehttp/guzzle/src/Handler/CurlFactory.php","line":158,"function":"createRejection","class":"GuzzleHttp\\Handler\\CurlFactory","type":"::","args":[["GuzzleHttp\\Handler\\EasyHandle",["GuzzleHttp\\Psr7\\Stream"],[],null,"*** sensitive parameters replaced ***","*** sensitive parameters replaced ***",7,null,null],[7,"Failed to connect to "FQDN of Nextcloud server.com" port 443 after 1 ms: Connection refused",0,"https://"FQDN of Nextcloud server.com"hosting/capabilities"

Daft question maybe, but is the rightdocuments server actually running? I had a lot of issues during initial setup of this.
For me (Ubuntu VM) I can run systemctl status php8.1-fpm and see 6 lines referring to richdocumentscode, coolwsd and coolforkit when it’s alive, in addition to at lest a couple of php-fpm: pool www processes (quite often far too many pool processes, but that’s another issue… )

In my case all my launch & connect problems were down to being clever and attempting TLS termination at a proxy, which only went away when I configured proxy-nextcloud to use TLS too.

The other obvious question is what might have changed just before it stopped playing nicely…

Hello @szaimen , I’ve reviewed the post How to debug problems with Collabora and/or Talk · nextcloud/all-in-one · Discussion #1358 · GitHub

here is output from the cmd

curl -vvv https://$NC_DOMAIN:443/hosting/discovery

Hello @szaimen , wow that seems to have fixed the issue, thank you. Can you explain why this fixed the issue? I thought that the host file needs to be populated.

the hosts file was configured below, and I removed both entries, leaving the host file with no hosts.

127.0.0.1 localhost
127.0.1.1 FQDN.com