2400MHz is DDR4.
1600MHz is DDR3.
Envy X360 has several model variants in it. DDR3 should 1.35v (DDR3L) for all DDR3 model variants. Does not support standard 1.5v DDR3.
So, the DDR3 that you found will not work your laptop.
Check memory selling websites with your model number, they should give you a basic information on what to upgrade with.