I'm sorry he's not doing well.
I'm going to tag in @Saaniya to help as well. She is in India so if more familiar with products, feeds, etc. that you may have available.
Are you providing grit for your chick too?
Welcome To BYC
Can you please post some photos of the chick and his poop?
What do you feed including treats?
What does his crop feel like?
Where are you located in the world?
Have you tried giving him drops of water to see if he will take them in. If he's not drank in 3 days, then he's...