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Comment by nabdab | Hacker News Reader

I had the exact same experience at the bitcoin only cafe paralelni Polis in Prauge. Only since they refuse to take cash I was left in a pinch. One of the people who worked there offered to spot me.... only to then adjust his balance which was registered on a piece of paper denoted in czk. Because as he said “the rate fluctuates so much and it takes so long to transfer that most who here just do one large transfer at some point and then run off the tab”.

Af far as proving that a bitcoin only cafe is viable it’s nothing but a PR scam. And I truly doubt that the people who’s balance was on that sheet actually went to the trouble of converting czk to bitcoin and then have the staff jot down the current rate equivalent czk. Most likely they just pay cash, and keep the facade up so media can’t claim their bitcoin only cafe is failing at being bitcoin only.

Good coffee though, just not worth the hassle.

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I already had bitcoin (and lightning) on a few different wallets on my phone and was able to pay at Paralelni Polis without any friction. It was easier than using my card because I didn't have to sign anything, scan the QR code in my hot wallet and it was done instantly. I think the step of getting Bitcoin is usually where the friction happens because you usually have to wait for a certain number of confirmed blocks (10 minute intervals) before you can send bitcoin from a new wallet.

I wished they had Lightning set up at Paralelni because to me this is even cooler for Point of Sale systems.

It doesn't matter the age of your wallet. Without waiting for other blocks to write your payment you run the risk of a double pay leaving you with nothing. e.g. I buy some coffee and then immediately send all funds from that wallet to my other wallet. If the 2nd transaction gets recorded first, the first tx won't happen.

This requires colluding with a miner, since nodes will reject a transaction that spends the same output as a transaction they've already seen. For a small payment like a coffee, it should be enough to check that the transaction has a reasonable fee and wait 1 second to see that it has propagated through the network.

The double spend problem with zero-conf payments is about equivalent to people making fake bank notes. It's possible and maybe a problem for small transactions (large TXNs people wait around for a few confirmations) but its stealing and just as illegal as any other form of theft.

> I didn't have to sign anything

Hmm, I guess you are american (with a magstripe card?) traveling in the EU? I never had to sign anything when paying with card here.

Having to put in a PIN is even worse than signing.

You don't even have to use the PIN if you are using NFC and paying under 500 CZK.

Yeah, true. Apple pay should get rid of this limit too, but some countries have fucked PoS configs.

I believe it’s set by law and not by Apple. IIRC when I was in Iceland it was 5000 ISK (roughly 50 dollars) for every single machine in the country. Over that you have to use the physical card or enter PIN/signature if the machine supports it (none of the ones I used in Iceland supported entering after NFC so I ended up having to use the card). Since everything is expensive as hell in Iceland it kind of diminishes the utility of the NFC a bit.

Edit: Actually after I typed above out I found a chart that has the limits: https://merchantmachine.co.uk/contactless-limits/

Apple Pay is authenticated and completely different from normal contactless payments which are unauthenticated.

Misconfigured terminals just happen to be really common, so sometimes it’ll work and sometimes it wont.

Why didn't this cafe use Lightning? Retailers: if you're going to take crypto, do the smart thing and use Lightning for BTC or xDAI for Ethereum. I'm just a crypto-enthusiast and even I know you don't use Layer 1 for transactional payments.

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