I purchased a pass lifetime Plex, but i cannot connect my account from my iphone.
Strangely, before the premium pass i could connect from my iphone to my home network and now the PC which is the media server shows “offline”.
But the PC server can be accessed normally with my apple TV…
That sounds as if you’re using different accounts. So in case your server is now linked to account A with a Plex Pass, your other account B will certainly no longer see the server (unless you actively share your libraries with that account).
Assuming you want to use just that Plex Pass account…
Open Plex on your iOS device
Go to Settings > Account
Click Sign Out
[probably overkill] Force-quit the app and restart it
Sign into the iOS Plex app using the credentials of account A (the one with the Plex Pass)