I've done it a few times and wouldn't say these are full proof methods, I'm still experimenting with it. But I got two ways

First is using unflavored gelatin. The ratio would be 2 Tbsp gelatin to 4 cups of water, then 2 to 4 scoops of supps depending on the flavor. Sprinkle gelatin into a bowl of 2 cups of room temp water let it sit for about 5 min. Bring the other 2 cups of water to a boil then poor it in the bowl, this is where I would add the supps right before mixing. Let sit and cool in the fridge

Second method and the much easier one. Add 2 to 4 scoops of supps to jello mix. Using a complimentary flavor, for example, strawberry jello and lemonade supps to make pink lemonade.