How can I provide and activate the WPMU Dev dashboard plugin to my clients site?

I am an Gold member of WPMUDev and its says I can install and activate wpmudev dashboard plugin to maximum of 1k sites in total.

So one of my client just asked me one plugin and I gave him the copy of the plugin. But when he installed the plugin it asks to either register for a new API or to Login with the username password if you already have an account.

I just want my clients site to use WPMUDEV dashboard plugin and from there he can install all required plugin and can use support, so how can I do that.

Or is there a different way like first I have to add the site of my client to my dashboard and then he will be able to use or I should provide each of my clients to use the login details to make work the plugin?

Help me out here please.