Quick connect synology

  1. Don’t use QuickConnect for anything related to Plex remote access. That’s due to fail in almost all common use cases.
  2. Are you trying to access your server remotely from a mobile app? For those you’ll need a Plex Pass membership or the dedicated remote watch pass

Did you 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.