This NIP is not yet in main. Here is an overview of PRs referencing this NIP. 
NIP-68 Lightning Debit Requests OPEN @shocknet-justin
[NIP-68] Client App Registration via Nostr for Delegated Auth Flows OPEN @jklein24
Shared replaceables via Event-owned keys OPEN @vitorpamplona
Shared Replaceables via Shared D-Tag OPEN @vitorpamplona
NIP-68 & NIP-69 - defined vocabulary for content warning & reporting (NIP-36 and NIP-56) CLOSED @rabble
NIP-068 Blinded Nostr Assets OPEN @kinakuta-co