If I'm understanding OP and others who are having the same problem as me, we can all find the link just fine we're just struggling to find where the 'Care' section is to add our partners to the Mailing Address as Nam suggested, and it doesn't give too many details on that in the link provided, only how to edit Phone and Email. I thought perhaps we're just meant to add it to the mailing address, but I can't find where to update that as it's not in Contact Details, even if you switch off eBilling. ...
