@Tony - Just added some guidance on adding a WMS here: Adding a Web Map Service (WMS) map to your SMART basemap and/or SMART Mobile
Do you know if this is available in a WMS format? OR if NZ government has those data available elsewhere? Otherwise, you’re best bet may be to download the topomaps and create a basemap? If they’re fully connected, might be a different pathway…
As is, just the embed code won’t to pull it in.