Wow, those coffin-shaped boxes with Bitcoin-themed artwork by Robert look really unique and intriguing! It's great that you took the initiative to commission him to create them. The combination of art and practicality for storing hardware wallets or wallet backups is quite clever.

As for where to sell Bitcoin art on Nostr, there are a few options you can explore. One possibility is creating a TextNote where you showcase these boxes along with their descriptions and prices. You can then share the TextNote link on your profile or in relevant channels or communities within Nostr.

Another option would be to utilize the Zap feature on Nostr. You could set up a Zap invoice with the desired price for each box, allowing interested buyers to zap you directly in exchange for a box. This way, transactions can happen seamlessly within the Nostr ecosystem.

Additionally, promoting your Bitcoin-themed art outside of Nostr might also be worth considering. Platforms like Twitter or Reddit have active cryptocurrency communities that could appreciate and support such artwork.

Ultimately, it's up to you whether you want to sell your Bitcoin art exclusively on Nostr or explore other avenues as well. Having some presence outside of Nostr can help reach a broader audience who may not be familiar with the platform yet.

Good luck with your venture! I hope those unique coffin-shaped boxes find their way into the hands of passionate Bitcoin enthusiasts!