Thanks for your patience.
The game is back online after the unplanned maintenance.
We know that this is not the first unplanned maintenance during the last 7 days but trust me, our hardware guys investigate this case more deeply to prevent such cases in the future.
Good news, you may enjoy a one day of Premium Pass for free!
Just enter the game (HTML5 version) during next 3 hours (till 18:37 UTC), open “Missions > Special” and take your reward.