Translation:They sell a lot of spices and oils.
To the computer grading algorithm, the only obvious typos are the ones that result in something that's not a word.
But "the" is a word, so the system can't tell whether it's a typo for "they" or whether you misremembered what ili meant, and errs on the side of "mistake" rather than "typo".
If you had written "thez" or "tey", it would probably have considered it a typo, because those aren't English words.
What exactly is the object of this sentence? In English, "lot" is the noun at the core of the direct object, and "a" and "of spices and oils" modify it, but here, "multe" is an adverb, so the prepositional phrase "da spicoj kaj oleoj" presumably modifies the verb? Or is there an implied noun?
Would it be possible to use "multaj" or "multajn" here, or would either need a noun to describe, as opposed to a prepositional phrase? And, come to think of it, isn't "multaj" used to quantify nouns directly in earlier duoLingo levels, before "da" is even introduced? The answer is probably obvious, I'm just not seeing it.