Template Not Responsive

Hello

I took on a website for a client, and I did not develop the original template.
The client has asked me to make it responsive, and I've done that, using the exact same procedure each time to make a layout.

Now it works perfectly, as it always does, for desktop and resizing the window. I use Responsinator to check the responsive side of things, and it's never let me down; however, it turns out that the site isn't actually responsive when it comes to genuine mobile devices, and I am at a loss.

I cannot even get to the source/developer tools when mobile either, so I literally have no idea other than to rebuild the site.

Nevermind - got it sorted. The viewport config was missing. This is why I don't like taking on other people's work :-D