I have applied both organic manures as well as chemical fertilizers to the sappota (Chikoo) tree, which is nearly six years old. Even though it has grown well to a height of more than 20 feet with several branches, it is not yielding any fruit so far. Initially, (3rd year) there were few small fruits but thereafter there is no fruit at all.
Sappota Tree Not Bearing Fruits
Certified GKH Gardening Expert
If the tree does produce flowers but no fruit, this could be a pollination problem. You could try hand-pollinating if you are not doing this already.
If there are no or very few flowers, you could try adding additional phosphorus and potassium; see this article for advice:
If there are small fruits that fall off the tree, this could be the problem: