Is it better to pay off debts first or to give out charity, and is it permissible to give Zakat from the amount allocated for the poor, or must it be given from the principal amount designated for debt repayment?

Repaying a debt takes precedence over voluntary charity, because it is an obligation, and it absolves one's responsibility. It may even be forbidden for someone in debt to give charity if it prevents them from repaying their debt. The money designated for debt or charity is subject to zakat (2.5%) if it reaches the threshold (nisab) and a full year (hawl) passes over it before it is spent. If the amount (500 pounds) is a vow, it is not permissible to count it towards zakat; rather, zakat must be paid separately, and the vow charity must also be given separately.