What is the ruling on the money I received for designing a reporting system for a foreign school, if it was discovered later that some of its financial transactions involve usury in the event of students' late payment, knowing that your work did not include designing the usurious payment system?

There is no harm in working for this foreign school as long as the work itself is permissible. The school's requirement for latecomers to pay an interest-based charge does not affect the permissibility of what is taken from it. This is because the Messenger of Allah, peace and blessings be upon him, and his Companions used to deal with the Jews in Medina despite their practice of consuming usury. Furthermore, the imams have agreed on the permissibility of trading with people of war.