When creating a virtual account, you'll see a "Commission rate" field.

This percentage determines the portion of incoming funds to a virtual account that will be automatically redirected to your primary account.

In other words, if you just want to fund the virtual account with no other conditions, you will want to set this value to 0.

In the above example, the virtual account has a commission rate of 10%.

This means that if $100 is deposited to the virtual account, the primary account will receive $10 and the virtual account will receive the remaining $90.