After we decommissioned PV tuning, we offered the ability to add a second free Rooftop PV site to our 'hobbyist' / 'home PV system' users.
However, your 2nd PV site must be at the same location as your first site. If you receive the following error:
([latitude value], [longitude value]) is not within a close proximity to your existing rooftop site
You are attempting to add a 2nd site too far from the 1st (original). Check the latitude and longitude of your existing site, and use the same values to add your 2nd site.