I would make sure you have one female and one male. Do you have pictures? The male and female can both have red bellies. The male is normally longer, while the female is shorter and rounder. The males dorsal fin is more extended and will come to a point, while the female is rounder.
Here is a pic of my male and female.
Here is the male. (which I still have). Unfortunately, one day he went crazy and killed the female off.
The female is on the left and the male is on the right.
I set up clay pots and they never spawned in them. They spawned underneath the driftwood. This picture is somewhat blurry, but this is underneath the wood.
This pair gave me 4 different spawns. The night before they spawned, I did a 50% water change and replaced the water with slightly cooler water then what was in the tank already. Apparently that helped.
Here is a recent picture of the very last spawn. I'm still growing them out to sell.
I am certainly no expert, but I have certainly experienced a lot with breeding Kribs if you would like to hear more. Just let me know.