cashapp is a payment service + exchange + custodial wallet in one

a hot wallet can be integrated in nostr clients, but it's still a lightning wallet running on Bitcoin and the issue you have is not related to that.

*if you want unrestricted buying -> use **decentralized** p2p exchanges like Bisq or Robosats

*if you want unrestricted spending -> use any hot wallet not tied to a KYC exchange - find on/off-ramps (e.g. azteco giftcards) if the shop isnt accepting bitcoin yet