The last verse to be revealed was the verse on usury, and the Messenger of Allah ﷺ passed away without explaining it to us. So leave usury and whatever raises doubt.
حدثنا نصر بن علي الجهضمي حدثنا خالد بن الحارث حدثنا سعيد عن قتادة عن سعيد بن المسيب
إن آخر ما نزلت آية الربا وإن رسول الله ﷺ قبض ولم يفسرها لنا فدعوا الربا والريبة
[Its isnad is daif]. Ahmad narrated it, 1/36, from the hadith of Saeed bin Abu Aruba, "Qatada narrated to us" with the same wording. Ismaili also narrated it, as in Musnad Farooq, 2/571, and regarding its isnad, see hadith no. 175 for its defect. It also has another route through Ismaili, which is daif.