While your balance is twice your credit (bonus), the credit remains untouched in your account. For example, if you deposit $2,000, you will receive $1,000 as a bonus. Then, if you earn a profit of $100, your balance will be $3,100. When you withdraw $100 from your account, your credit won’t be deducted because your balance is still twice your credit.
However, if you withdraw more than $100, for example, $200, your balance will change from $3,100 to $2,900, and your credit will change from $1,000 to $950. It means that if you have $2000 as a balance and $1000 as a credit on your account and you withdraw $1000 from your account, then $500 will be deducted from your credit too.
Remember, the bonus supports your required margin and open trades. If your balance hits zero, the credit is automatically removed.