Tags system for a Post on Phoenix app

Hello guys, In my app I want to implement a tags system where post can have many tags, and tag can have many posts. I have seen couple of ways to do this but I struggle to make it work on the Liveview side. I want admins to be allowed to create tags in panel, and When admin edits or creates a post I want to display list of tags that you can select or check, and they will be associated with this post. I tried following this guide now, but struggle with how do I make the liveview form for post work: Constraints and Upserts — Ecto v3.10.1