FYI to all: we have already updated this to the plural "letters," but it often takes time before the update we make on the back end are reflected to users.
To my knowledge, "epistulas" can only be plural. I reported this sentence. We shall see!
According to OLD s.v. epistula 1b it appears that the plural can in fact refer to a single letter (suggesting "perh. on anal. of litterae"), but as far as I can see there's nothing saying that it can't be an actual plural either, so "letters" should also be correct. (I just got "We send letters to the orator." rejected and reported it.)
That seems to be a common problem through this section. To improve the course, deliberately answer it "incorrectly" each time and report it.
The tiles gave me a letter and it was marked correct. I didn't report it as I didn't read this thread first. Will report if I meet it again.
"We send the letter to a orator." was accepted. That's incorrect English. It needs to be 'an orator'. And 'epistulas', that's plural accusative, and we're only sending one letter?