There is an in-game currency Black Gems (BG) used for all servers.
After a trial period, the player receives a notification of the minimal mandatory payment of 100 BG. To make a mandatory payment, you should use one of the available payment methods in the mandatory payment notification window. If the available payment methods are not suitable for you, you can transfer 100 BG to the server in any other way (including a gift from another player). The system will consider such a payment as mandatory, withdraw the BG from your account and you can continue the game.
ATTENTION! The mandatory payment is not credited to your account as Black Gems!
You can always add BG from the Portal to any server.