This NIP is not yet in main. Here is an overview of PRs referencing this NIP. 
NIP43 Authentication Delegation OPEN @monlovesmango
Add relay access requests OPEN @staab
Secure DM CLOSED @arthurfranca
Shared Key DM CLOSED @arthurfranca
NIP-43: Bounties OPEN @ChristianChiarulli
NIP-43 - Fast Authentication CLOSED @arthurfranca
NIP-43: Bitcoin-Funded Public Keys to Prevent Spam CLOSED @brunneis