What are the specific purpose of built-in nostr nsec there ? To receive nostr notif push whenever users receive pending payment to their LN address ? Anything else? 

 https://docs.zeusln.app/for-users/embedded-node/faq#why-do-i-have-to-enter-in-my-nostr-nsec-key-when-setting-up-a-zeus-pay-account 

 Ahhh thanks man!