Give water with apple cider vinegar in it.
It will give an immune boost and keep the packed stuff int he crop from ferminenting.
Wait until tonight to give back some crumbles - NO grit! - and keep up with lots of water.
1 quart of water with 1 tsp ACV.
At 3 weeks old the chick only needs chick starter.
STOP feeding it grit. It is not needed.
The crop is probably full and needs to pass it.
Withhold all food and only give lots of water for 6 hours and see if it goes down.
If it does, give ONLY chick starter and water.
If it does not, with...