This NIP is not yet in main. Here is an overview of PRs referencing this NIP. 
70.md:use relative link MERGED @RandyMcMillan
relay-based event access-control with the `["-"]` tag MERGED @fiatjaf
NIP-70 - Collaborative Events OPEN @leandro21b
WIP:  NIP-70 Signature Requests and Responses using Nostr CLOSED @mgravitt