Hi, I have the same issue.
When i try to activate my licence key there is a text message : “invalid request”.
I have never used my licence key or this plugin in other website and i don’t understand why and where is the problem.
You can access to my website as an admin : http://lesfranchouillards.com/demo/
Login : wcvendorspro
Password : wcvendorspro
Thank you for your answer.