I created a new user, set as Active. When I create a new site I can nog select this user Client. What could be the issue?
You have to create the client in the client module. Never create users in the cp users list manually as cp users are not clients and so can not be selected or used to create anything in ispconfig. Please delete the user in the cp user list that you added manually and then create a client instead.
I don't know why I didn't do it in the Client module. Indeed I did it in the CP. Tnx for your fast answer!