How to bring up the mobile keyboard on Iphone

I've been having trouble getting up the mobile keyboard for an input field in a game i've been making. I've looked through all the documentation and I've been through unity answers but everything that I have seen, although most of it seems to pertain to what I need, does not work. I've tried using the function TouchScreenKeyboard.Open in my code but nothing happened. All I need is for a user to be able to type in their username to login, but I cant seem to get the native keyboard on the phone to pop up so that they can type. So if anyone could help it would be much appreciated, as this has wasted over 3 days of my time now.