> Question about LN, if I have funds in a Muun wallet, can I send to a friend with a CASH app wallet? The language makes it sound like we have to be on the same "payment channel" so I would guess the answer is no. But then how are retail checkouts meant to work, should a retailer set themselves up with a muun wallet as well, or is there a way for LN channels to interact?

Yes, I just tried it: this is what I did and it was all pretty seamless.

- I sent out a desired amount to my muun wallet using a LN invoice from my CASH wallet and it was received instantly for no fees.

- Once in my Muun wallet I sent it back to my CASH app bitcoin wallet using a Segwit address, as you cannot currently create a LN invoice within CASH.

So, it seems that while CASH supports LN it is only for withdraws and not deposits; this could possibly be added later as a feature by the CASH team, though. But as of now, only Segwit layer 1 address deposits are available to a CASH wallet.

Still, I paid ~7 cents with a 1sat/byte tx and it arrived in the next block since the mempool is clear using a segwit address.

If a retailer wants to take payments via BTC and LN they have two choices: use custodial wallets like Muun that support both Layer 1 and 2 protocols and move to a secure wallet where they hold the keys. Or invest in running their own nodes and a deploy a system that works for them.