The dot at the bottom right says whether SyncNow is talking to its server right now: green Online, red Offline, or grey Checking… before the first answer. When SyncNow cannot reach its server, the left side says Not connected to SyncNow, followed by the reason; otherwise it is empty, apart from the confirmation of something you just did, which disappears after a few seconds.
Move the mouse over the dot to read why SyncNow is Offline, because each cause has a different fix: the certificate presented for the address is not valid, the address does not resolve, nothing answers (no internet, or the server is down), the server took too long, www.syncnow.it answers but the SyncNow service is not there, or the hosting is rate-limiting your PC and SyncNow waits before trying again. Only an answer from SyncNow itself counts as Online, so an error page from the hosting does not turn the dot green.
Problems of a single project are not in the status bar: they are on the project's row, with a yellow sign in place of its icon, and next to the project's name when you open it. While SyncNow is Offline, agents cannot open projects or change files, because every safety check runs on the server. See What does a yellow sign or FTP sign-in rejected mean on a project?.