Your customer needs to do the following:

1. They need to install the Universal Edition not the Standard Edition.  My guess is this is the problem, but it is possible steps 2 or 3 below were not done properly.  Although Universal Edition is installed, when they login with the email address associated with the Standard Edition it will automatically disable the Universal Edition features but permit the customer to use the rest of the product.  You know you have the Universal Edition installer if the .ZIP file ends in "UNV-EN".

2. When installing the Universal Edition it is important to install all the features, such as PowerServer Toolkit and PowerServer itself.  Otherwise, the most you'll be able to see is the Cloud Edition features even though your customer is logging in with a Universal Edition subscription email address.

3. Then simply login with the email address associated with either the Universal Edition or Standard Edition to get the appropriate features.  And to switch between the two, you would first need to log out of one email address and then log in with the other email address.  The following video tutorial shows how to do this: https://www.appeon.com/developers/library/videos/license-activation-tutorial.html