The consistency and viscosity is intentional, and artificially induced.
The usual response to this conundrum is to “add more water”. Which basically means that if it’s unpalatable to you at the current thickness, use less powder, more water, and maybe even split all of that up into two shakers.
I think using the tool is useful. The OP is aiming for 500 calories but it suggests 4 scoops is 608 calories. Also 760ml of water for that 4 scoops. Since the 760ml of water is pretty much an entire shaker that would leave no room for the powder. So 4 scoops topped up with water will be less than the recommended amount of water and, therefore, thicker. So just using the tool explains the problem.
Depending on how accurate they want to be you can see from the tool 3 scoops is 456 calories, 570ml of water. That leaves room to shake, add/subtract water or huel. So seems a good place to start. But the best tip is to use the tool.