Selective disclosure
Prove one payment. Not your history.
A receipt holds one payment's salt and memo. Anyone can check it against the book on Elysium. It reveals that payment's memo to whoever you give it to; every other link keeps its own salt and stays closed.
Check a receipt
Paste the receipt JSON or a receipt link. The check reads the book on Elysium: no account, nothing stored. A receipt reveals the memo of one payment and nothing about any other.
The book is not deployed yet, so no receipt can be checked against the chain here.