Refresh the server list: in Happ, tap the ⟳ (circular arrows) icon in the subscription header — the server list updates. If that didn't help — reopen the app.
Re-issue the subscription (if it stopped working entirely): on lk.surfingvpn.com → the Home tab → on the subscription card tap "Manage" → "Re-issue subscription". The old link stops working on all devices — after that, add the subscription to Happ again.
Add the subscription to Happ again — with the "Connect" button on the "Connection" tab. Or manually: in Happ tap "+" in the top-right → paste the link from the clipboard or scan the QR (get the link and QR on the Home tab, in the "Connect" panel).