It seems to be impossible for a Charge site administrator to enable a user to see his charger in his app if the access level for the site is "open to everyone". The open access level is the most relevant/convenient for a site with individual locked garages.
It is possible to add the user as whitelisted for his charger, but when the access level is switched back to "open", his charger in the app is not connected anymore.
Chargers are v240.
you can add the user in the whitelist for the site and that will work until its fixed.