I'm curious about the legal implications of this. For example:

- In the EU, a consumer has 14 days to withdraw from a contract that you have concluded online, unless the consumer explicitly waives this right during the purchase (so your payment required page will need an explicit statement about this).

- I'm pretty sure in the EU, and probably most countries, you must receive an invoice, even if it's for a 1 cent purchase.

- You might also have to pay VAT on these transactions, which will need to also be included in the invoice. This is especially important for B2B purchases, because companies can claim back VAT.

- What happens if I complete the purchase, but there is an error in the response returned by the website? I.e. between the events of my purchase being confirmed and the server returning the response, the server dies. What recourse do I have?