You seem to be confusing paying for Signal (there is no way to pay for it, but you can donate to the foundation) and exchanging money with your friends.

As Schneier says, that could be implemented in a separate application, not the core Signal product.

Signal just added a bunch of crowbars to the people who want to crack it open. Money laundering and tax evasion are seen seriously and there's generally more people doing it than, for example, planning terrorism.

AFAIK crypto is the only way to get private and secure payments. Any other payment mechanism wouldn't fit the ethos of Signal.

And why exactly does Signal need to be a kitchen sink app? What's next, CandyCrush inside Signal?

What I meant was that Signal can solicit payments as part of their mission. Either through donations, or by selling access to more features. There's no need to involve financing through the use of the product itself, any proceeds of which will not go to Signal anyway.

Signal doesn't sell paid features, Signal is adding a payment platform. So future apps and/or users can exchange money/crypto.

Yes, and I would argue, with Schneier, that that's a bad idea, for all manner of reasons, not least that it will widen the legal attack surface by a lot.

The question is more whether it needs to support private and secure payments in the first place. That is, legally and ethically, a whole different beast than private communication.