"I have change."
Translation:J'ai de la monnaie.
Is it because one means "cash" and the other means "change"? I made the same mistake, by the way.
monnaie → "change" or "currency" (in the sense of coins) is a mass noun so requires a partitive article. As monnaie is feminine, the partitive article is de la.
Why not "J'ai des pièces"? As in "Tu me rends trop de pièces" that also appears in this course?