So am I understanding correctly? 少ない here means insufficiently few, and thus 少なくない is not insufficiently few--in other words enough?
Why is .... けっこう です Wrong?
Why not 足ります?
I had learnt "enough" is "じゅうぶん（だ）" and "足りている".
Just as in English, there is more than one way to skin a cat. (My apologies to my beloved feline friends.) There is more than one way of doing (saying) something.
Literal translation: "There is not little coffee"
Meaning "There is enough coffee"
This one made me think, :D