Can I remove full screen mode?
Yes, you just have to press F11
I get the message Order Error when I try to make a payment ...
Login to your account via google chrome without playing, then try again.
Do you have a connection problem?
Press the ALT key on the keyboard, click « Edit » and then « Clear App Data ».
Some essential shortcuts!
First of all click in an area outside the game (photo below)

Zoom by holding down the CTRL key and then the + key.
Zoom out by holding down the CTRL key and then the – key.
Close the client by holding down the CTRL key and then pressing the W key.
HOW TO CLOSE YOUR CLIENT
Hold down the CTRL keys and press the w key.