I’m interested in a how-to too. Def still early but I’m looking forward to potentially using this as a merchant. I think nostr:npub155m2k8ml8sqn8w4dhh689vdv0t2twa8dgvkpnzfggxf4wfughjsq2cdcvg had support for it for a while.

https://docs.btcpayserver.org/Payjoin/