I can't change Wi-Fi settings on the G4...

[jc909uk]

I've just picked up a new LG G4 and I've been trying to change my DNS settings. However, when I go to "Modify Network" I'm given all the options but the "Save" button is greyed out. No matter what I do or input, nothing allows that "Save" button to become active. I've done exactly the same thing with my Galaxy S4 and never had this issue. Does anybody know how this can be sorted?