Snapt Aria has two categories of pricing, these are Standard and Enterprise.
An upstream refers to any server that sits behind your Snapt Aria virtual Load Balancer (web servers, app servers, etc.)
On our Standard pricing plans your license will limit the how many backends/upstreams you can add ( the amount increases with the higher the tier of Standard).
On our Enterprise licenses, you are unrestricted as to how many backends/upstreams you can have.
Please take note that an upstream and a backend are the same things.
If you have further questions then please email us at firstname.lastname@example.org.