Device not online usually have below reasons:
1.Device is not connect to internet.
2.If device connect to internet,  the SIP message or port from internet is block by the router of firewall.
3.If device connet to internet, and no blocked by firmwall, then must be device under SDMC mode.

To make it only,
1.try to reset device. (in case it is under other mode, and can make device initial to make require to cloud to conenct again)
2.try to add white list of akuvox servers domain to your router.(attached instruction)
3.check your network connetion. （If it is Android based device, you can do that by open browser, check whether able to search internet.)