In the deposit account section, your current balance can be found in the top upper right of the screen. A balance that is positive indicates there are funds still available to be spend. A balance that is negative indicates that the deposits have been depleted and a top up to the account is needed.
In the detail section for the deposit account, an invoice is represented as a negative number, meaning a reduction of your balance. A deposit is represented by a positive number, meaning an addition to your balance. There may be a situation where an Invoice is a positive amount, and this would indicate that an invoiced amount has been reversed/removed, therefore adding the funds back into your deposit account balance and available to be spent.