How can the straight path of truth be clarified to a friend who follows the Zaydi doctrine, knowing that this doctrine is classified among the doctrines of innovation (bid‘ah) but is closer to Sunnism?

The people of knowledge should undertake to establish the proof and remove the doubt concerning the people of innovation. If you are qualified for that, then you must clarify the truth to your friend with evidence. Otherwise, direct him to a trustworthy scholar, or help him with books that are beneficial on the subject. Allah has benefited many people from that group through the words of scholars, and they have returned to the truth and supported the Sunnah.