"One more time."
This example is bad. You need a verb for imperative. 再来一次 is the standard usage.
In this exercise it would be helpful if "再" appeared somewhere in the hover-over hints (As of 11/21/17, it appears nowhere. I have reported it.)
The hover-over hints also don't even contain the desired answer.
This seems to fit in the category of "not there yet" parts of the course.
I suspect they're being cute and introducing the words for repetition when we're repeating things
Why is there the first character? What does it mean? It doesn't translate, when you tap on words in English