What did you try and to what exact outcome?
„Trying everything“ is rather vague when it comes to troubleshooting a technical problem …
Do you mean you did already have a look at the related troubleshooting support article?
https://support.plex.tv/articles/200931138-troubleshooting-remote-access/
There’s also a guide with some more details on how to troubleshoot remote access issues…
When you mention certificate issue… did you assign an individual server certificate to your Plex Media Server?
