Erythritol is listed under carbs but only has 0.24 calories per gram. So if those 12g carbs are all from the erythritol, that would only be 12*0.24 = 2.88 calories, which would be rounded down to 0 on the nutrition label.
The 12 carbs are most likely from erythritol. As for the concentrated lychee juice, I’m not too clear on what that is exactly, since it’s also labeled under natural flavor, which generally does not have calories.
Could be a sugar alcohol like erythritol which is absorbed through your body and doesn’t metabolize the traditional way
https://www.webmd.com/diet/what-is-erythritol#:~:text=Calories.,into%20energy%20in%20your%20body.