Adding 3rd RAM on Zbook 15 G2 / 16GB to 24GB

[Matt_2018]

Have added an addition 8GB RAM (a 8GB DDR3L 1600MHz (PC3L-12800) SODIMM) on my HP Zbook 15 G2, run BIOS to check it. But when saved/booted in to Windows, does not go through. Help needed to find issue

[Huffer]

My G3 has 4 RAM slots does your G2 also? I believe that third module has to be done into a specific slot. What slots are now populated with memory? 

[Matt_2018]

Yes, it has 4 slots. existing have 2 x 8GB. For the additional 3rd 8GB, have placed it on the slots easily accesible below the computer upon opening the cover.

As I read on the manual there is another slot below the keyboard, have not open that out yet.

Would it make a difference if I try it on the slot under the keyboard? 

[Matt_2018]

Forgot to answer, looks like 1st 8GB is under the keyboard and the 2nd 8GB under the computer. So one slot available on both under th computer and might be the same on the slots under the keyboard.

[Huffer]

Here is the Manual:

Manual

It does not specify where to put the third module. If it is not working on one slot I would put it in the other as a logical next troubleshooting step.