That would explain it. I mean if your provider provides you with a proper certificate, you can also use that. But often times it’s just a temporary self-signed placeholder that’s only good for development and not valid.

Where did you get your certificates from and what’s the exact error message? Maybe you’re using self-signed certificates. Those don’t get accepted by anyone else. Your path doesn’t look like the default letsencrypt/acme path…

I have little experience with windows (web)servers and more with linux.

I have no idea why someone would want to set-up or manage a windows server. It’s just pain if you previously did it with linux. Everything sucks. Where to find log messages, how to upgrade a php version and get that used by the webserver, backup, maintenance, how to write short and useful scripts for maintenance, the mixture of config files and lack thereof, and it needs double the resources.

I wouldn’t do it in my spare time. I’d rather work on a way to get that OS in that VPS replaced… (My personal oppinion.)