If I invest $200 and start trading with this amount and after that I have a loss of $210, what would it mean?
It's impossible to have a loss of 210 $ which means that they offered you a bonus when the account was created and the "error" is caused by the loss of the money. Because of that the balance now displays -210 $. You can overcome this error by recharging your account with money. Log-in on the website and there will be the possibility to recharge your account.