Remove the Download ID before taking a backup / handing over the site. Remove all old backups; if you are passing the administration to someone else they don't need your old backups.
If these are non–options for you, come to our site, log in, go to Add–on Download IDs and regenerate your Download ID (it's the yellow button next to it with an icon that looks like repeat / recycle). You will need to update all your remaining sites with the new Download ID, though.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!