Getting subscribers through your getsoldlive.com URL
You can have your shoppers go to getsoldlive.com/[yourdomain] to subscribe. For example if your store's domain is asherkate.com, have them go to getsoldlive.com/asherkate
If this is the first time they've messaged your FB Business page, they'll see a "Get started" button:
Once they click it, they'll get prompted to subscribe to your live announcements by clicking "Get messages"
After they click "Get messages", they'll automatically get messaged whenever you go live: