i5 8600K - Cant go higher than 43 multiplier

[Dyewitness]

Hi Guys

I just took delivery of my new gaming rig and its great.
I thought i'd tamper with some Overclock settings ( I haven't done in a while )

I changed the Overclock setting to sync all cores and when I try to enter 45 (4.5ghz), I got an error about an N number and it wont go higher than 43.

Can anyone explain whats going on?

Help appreciated,

Chris

 

[Dyewitness]

What motherboard are you using?

Just found out the H370 mobo cant go higher than 4.3ghz (advised by OCUK)

Asus ROG Strix H370 F Gaming