Dropbox Backup Pro license?

I have been looking all over the plugin page and support pages but it is not clear if this pro license can be used for multiple sites?

I’m asking because at the registration page it is asking for the address of my website which made me concerned that the license is for 1 site only. I run a few sites for various hobbies of mine. I would love to have them all backed up but do not want to pay 40 bucks per site.