Add all the ingredients to a saucepan and stir until well combined.
Bring to a boil, stirring frequently.
Allow it to boil for 2 minutes, stirring occasionally.
Pour the jello mixture into individual serving bowls or glasses.
Refrigerate to set. It will take up to 2 hours to completely cool.
Keep leftovers covered in the fridge for up to 1 week.
Notes
Any type of fruit juice will do. You could also use half the amount of water.
I’ve never tried this recipe with agar flakes, but if they're all you can find at your grocery store, follow the package instructions to know the amount of them you need for 2 cups of liquid (480 ml).
Sugar is optional, but the vegan jello tastes better if you add some. Any type of sugar will do.