Under match options for weapons customization you put "customiSation"

Good work.

Release a patch please and fix everything else

<3

I think both are correct,one is english and one is 'murican

iPhone and Microsoft word say otherwise

In the future, after a etimology disgregation, the word "customization" referring weapons on a match is spelled with an "s" due to many misuses and finally staying like that.
Crytek already foresaw that, and implemented it on the game.

In the future, after a etimology disgregation, the word "customization" referring weapons on a match is spelled with an "s" due to many misuses and finally staying like that.
Crytek already foresaw that, and implemented it on the game.
Future-proof graphics were already Crytek's specialty. Enter future-proof spelling

Cyrtek used the British spelling not the American spelling but essentially both spellings are correct. The reason your spell-checker is saying it is wrong is because the default installation of MS Word uses the American dictionary. Try entering 'define:customisation' as a search term in Google (without the quotes).