G'day mate, Not sure how the clan side of things work. You should be able to just set one up then invite them but they will prob have to be signed up to the forums i doubt it will just go by gamertag. If you are having trouble adding them then get them to search for your clan name in the search bar at the top fight of the forums then at the bottom of that search result box it should show your clan. If they click on that it should take them to your clan page then they should see a join/request join button??