ASRock z370 pro4 Memory Question

RLGL wrote: The memory must be a matched set, by the manufacturer. You cannot mix and match. If you get 2 pieces of memory and later get 2 more pieces of the same part number, there is no guarantee they will work.

Thank you.   I appreciate your response.

But I'm not exactly sure I understand. This means if I am using all four slots, all four memory sticks must be exactly the same?

I'm not sure I understand the memory instructions in the manual.

I understand that memory needs to be installed in matched pairs.

But can I installed two different pairs?   That is can I install:

2 X 8GB DDR4-2400   Latency 17-17-17-39

2 X 16GB DDR4-3200 Latency

Or must all memory be exactly the same?