My question is regarding the authenticity of naad e Ali. I’ve been reciting naad e Ali my entire life but recently I came to know that the chain of narration is not authentic. Can u provide a reference? If there is no chain of narration, can reciting naad e ali be considered as shirk? How do I explain it to my non shia friends?

If the chain is considered by someone as weak or broken or unauthentic the wordings itself are so beautiful that to deny it due to any narration doubt is impossible just like dua e Sabah. Secondly asking help of Amir ul momineen in itself as asking Allah s.w.t. as he is among the most humble Servants of Allah s.w.t.
Thirdly it is narrated that Holy Prophet s.a.w.w. had uttered these wordings during the battle of Khyber.