Everyone's first bhakri falls apart. It is not you, and it is usually not the flour either — it is a technique built for wheat being applied to a grain that has none of wheat's structure.
The core problem
Wheat dough holds together because gluten forms an elastic network. Jowar has no gluten at all. Nothing is holding your bhakri together except starch, water and heat. Roll it like a roti and it will crack every time.
Five fixes, in order of impact
1. Use hot water. Not warm — properly hot. Hot water partially gelatinises the starch, which is the only binding you are going to get. This single change fixes most cracking.
2. Knead longer than feels necessary. Five to seven minutes. You are not developing gluten, you are working starch and water into something cohesive. It should feel smooth, not crumbly.
3. Pat, do not roll. Traditional technique is to flatten it with the palm, rotating as you go, usually on a damp cloth or a sheet of plastic. A rolling pin puts stress in one direction and it splits along that line.
4. Keep the dough covered. Millet dough dries out within minutes. Work with one ball, keep the rest under a damp cloth.
5. Hot tawa, confident transfer. Hesitation is what tears it. Lift and place in one movement.
And then the flour
Freshly ground jowar handles noticeably better than flour that has sat for months. Older millet flour is drier and more crumbly to start with, so you are fighting the technique and the ingredient. If yours has been in the dabba since last season, that is worth ruling out.