@Uwe:
To invite Friends to join at times the registration is not open. Only Power User can use them.
You aren't Power User, so they are currently useless for you. Anyway each user gets initially 4 invites, which he can use when getting the Power User status.
May I ask that you put this explanation on the Seedbonus for points page so that we darlings can be spoiled and to save us having to search through the Forum to find out what 'invites' are that we can exchange points for?! :hug: