Is receiving financial support for medical studies, on condition of repaying a percentage of future income, considered usury (riba)?

If the financial support is in the form of a loan and an increased percentage is stipulated, then it is outright usury (riba).

If it is in the form of an exchange, whereby the agreed-upon percentage is a compensation for the money provided during the study period, then it is a void contract that contains the defect of usury and ambiguity; this is because it involves an increase of money for money and a delay, along with ambiguity regarding the monthly income in terms of amount and duration. Therefore, it is not permissible to enter into this agreement.