Undetermined Gender Fischer's Bird, Healthy and Active

Hello, Type: Fischer Gender: Undetermined Health: 100% Cage: None (only transport cage); whoever buys it will get the nesting box along with the nest A pair of Fischer birds was purchased, and the female laid 4 eggs, all fertilized, but the cage door was left open, one bird flew away, and now I have this one left... I don't know whether it's male or female. However, its health is excellent, it sings well, and both it and the female built a nest, which still exists (see attached video). Price negotiable