Sorry for the question, I am new here.
Hi, it is one license by computer. You can change the hosname of computer in customer license area if you reinstall Duplicacy Web Edition.
If you have 3 computers, you need 3 licenses.
No, I have a license for one device but I want add more devices to this license.
You can’t.
You must buy a second personnal license at the half price of the first.
All informations are here ; Duplicacy
Thank you 
The secret was to put the current license key in the promotion box
Ohh … i see. I forget this 