The most common reason for agar agar to remain liquid and not solidify properly is due to higher ratio of water to the agar agar powder. To avoid this problem, keep to the amount of liquid mentioned in the recipe. If you wish to add additional liquid ingredients (such as juices for flavoring), remember to reduce the water in your recipe by the amount of additional liquid ingredients in the recipe. That way, you jelly will set well. Other reasons could be undercooking the jelly solution and insufficient time to set. If the jelly powder is not fully dissolved, the jelly will not set properly. Make sure to cook the jelly to a rolling boil point. And depending on the mold used to set the jelly, the time taken might differ. It will be quicker for wide and shallow mold and longer for deep molds. Always check by shaking the mold or pressing lightly with your finger. If it is no longer wobbly and is firm to the touch, it is ready.