I am so sorry. :hugs Sometimes a chick just fails to thrive for whatever reason and no matter what we do. It's still hard because they are so darned cute and precious. ❤️
Hiya, and welcome to BYC!! :frow
I would try getting it to drink or using an eye dropper to drip some electrolytes/probiotic water, like Hydro-Hen or Save A Chick. If you don't have any, try a small amt of honey mixed in water.
I'd add water to make a mash out of their grower if it perks up...