Hi.I have never heard of this refferal link,however the only way that i am aware of inviting your friend to your kingdom is to send him a message with your kingdom number and then once he/she permanently moves to your kingdom you can invite him/her to your clan,,however they will need drakkers to do this and if they are a new/ish player this may be problematic as drakkers are hard to come by in the game without spending real money, i wish  there was better news for you.

Good Luck