Foreigner

I think the fundamental difference between that experiment and the "suicide capsules" vs the death penalty is that in the *former the people going into it are doing so willingly. I imagine people undergoing the same procedure involuntarily will probably resist, hold their breath, panic, do whatever they can to sabotage the process, etc. The reason this method is rarely used to euthanise pets is precisely because of this - the animals get stressed (as many often do at the vet where they need to be for the procedure) panic, react, and it takes way longer than it should as a result.

Edit: edited for clarity

If you're in France there's the Carte Bancaire.

Edit: I've just looked into Revolut and they're UK based with operations throughout Europe, so they might be an alternative for online payments across borders.