What is the ruling on collecting debts for a financial (usurious) institution in exchange for a percentage of the collected funds, and is the income generated therefrom considered lawful or unlawful?

It is permissible to collect debts for a fixed fee or a percentage of the debt. This falls under the category of ju'alah (stipulated payment for a service) or wakalah bi ajr (agency for a fee), provided that the debt is not usurious. It is not permissible to collect usurious debts, such as debts from usurious banks, because that entails cooperation in sin and aggression. Scholars have agreed on the permissibility of taking a fee for collecting non-usurious debts, while it is impermissible to collect usurious debts or take a fee for them. The determination of the fee amount and the time of its collection is subject to the agreement of both parties. Accordingly, if the financial institution deals with usurious debts, it is not permissible to work in their collection.