PlayStation Network ("PSN") or the game's server may be temporarily unavailable. Please check the status of the game's server via its website.
If the servers are active, please run the Internet connection test at Settings > Network > Test Internet Connection and make sure you can connect to the network.
Update your router to the latest firmware. If possible, reduce the stress on your network by disconnecting any other devices that are connected. If this does not work, try again later as the server may be experiencing high volume.