Sforno on Deuteronomy 15:2/ספורנו על דברים ט״ו:ב׳

1וזה דבר השמטה, when G’d said והשביעית תשמטנה, (Exodus 23,11) the meaning was that you should also have a concept of sh’mittat kessaphim, releasing overdue debts by your debtor at the end of that year. The words משה ידו, “what is owed him as a creditor” in our verse make this pretty clear. [Furthermore, if the word מקץ means “at the end,” it is clear that this verse does not refer to the produce grown during that year. Ed.]