Child is taking out side food well so not an issue of low appetite, its about fussy eater. So no need to give appetite stimulators.
This medication are temporary effective and rebounding effect and that will not help in fussy eater.
Give food which he likes but make it at home. Make a twist in routine home made food like if he is not eating chapatis then apply home made tomato sauce and put vegetables in it and make roll or wrape if he like spicy and if he like sweet apply ghee and
sugar or fruits and make roll.
For complete diet only chapatis or milk or single item is not measurement, diet should be complete nutritional, healthy and freshly prepared which includes all type of foods (a full healthy balance diet dish).
Consult pediatrician or dietitian for further evaluation