Google have sent a message saying that we need to show their logo on the map.

How can we get that to appear?

I have got around the issue for the time being by adding below to the Additional CSS section..

img[src*="https://maps.gstatic.com/mapfiles/"], .gmnoprint.gm-style-cc {
 display: block !important;
}

This adds back the google logo and the Terms of Use.  Hopefully that will be enough for Google, but you should look at providing a proper solution to this given that using their maps does require these things to be included.