A vet trip is definitely in order to see if there are parasites causing the lack of appetite. That and stress are the most likely reasons for not eating.
Double check your temps to be sure there's a basking area of 95-100 and various temp zones ranging downwards to about 80. If he's too hot or cold he won't be able to digest properly and so might not be eating. Make sure the cage humidity is at least 60%, preferable more like 80 so that dehydration isn't complicating things. Use a digital thermometer instead of the kind they sell in pet stores which don't tend to be very accurate.
Also, make sure that your ig can hide while eating. Place food inside a hidebox, or behind a nice silk or plastic plant so that s/he doesn't feel vulnerable to predation. Keep the greens pieces very tiny so he can just grab the quickest little bite. Try a couple of different feeding stations so you can see where your ig prefers to eat. Many little ones like to eat high up in their cage as though they were nibbling leaves from the treetops.
When I have a new animal in the house I literally count out 5 tiny pieces of each type of food in the salad so that I can be absolutely sure how much they are or are not eating. Tiny little iglets will sometimes nibble away but such a small amount is gone from the dish that it looks untouched. It's also a good way to see what foods they prefer.
Smear a little baby food on his snout so at least he will lap up a few calories. Butternut squash is an excellent type as it's nutritious as well as tasty. You can also whirl up some greens in a blender to make your own baby iglet food as that is one of the best things they can eat.
Good luck and let us know how the poor little greenie makes out.
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