Bitcoin withdrawal records: what survives the payment
A Bitcoin payment cannot be edited afterwards, so the only thing left to work with later is the record of it. That record is smaller than most people expect: one identifier, issued when the transfer is signed, that points at a single entry in a ledger anyone can read.
This note is about what that identifier proves, what it does not, and what is worth saving before the cashier's own history has a chance to be the only copy.
What the transaction id actually is
A string of letters and digits derived from the contents of one transfer. Change a single detail of the payment and the string would be a different one, which is why it works as a fingerprint. The same string is shown by the wallet that sent the coins, by any block explorer, and, if the cashier is generous with detail, by the cashier.
Because the ledger is public, the id lets a stranger confirm four things about a payment without asking anybody: that it happened, how much moved, which addresses were involved and which block took it in.
What it does not prove
Who owns the receiving address. The ledger shows an address and a movement; it does not carry a name, an account number or the fact that a particular casino controls the address. That link lives inside the cashier's records and nowhere else.
That is the reason a cashier's history and the ledger are two different witnesses. The history proves what the operator recorded. The ledger proves what the network accepted. A question about a missing withdrawal is answered by laying one beside the other, and if either is missing the question gets longer.
What to save, and for how long
Four items, kept together: the transaction id, the address, the amount as it left and the time as the wallet shows it. A screenshot of the wallet entry covers all four at once and takes seconds. Export the cashier history occasionally if the account offers it, because a history shown on screen is a history the operator can change the layout of, or close.
Keep it for as long as the account exists. Questions about a withdrawal tend to arrive weeks after the withdrawal, when the details have gone and the only thing that can answer them is something written down on the day.
Short answers
What is a transaction id?
A fingerprint of one transfer. It identifies a payment on the shared record and can be looked up by anyone.
Does the cashier's history prove a payment arrived?
It proves what the cashier recorded. The shared record proves what the network accepted, and the two are checked against each other.
Why keep a record of an irreversible payment?
Because the record is the only thing left to act on. Nothing about the payment itself can be changed afterwards.
How long is a record worth keeping?
As long as the account exists. A question about a withdrawal rarely arrives on the same day as the withdrawal.
Related pages
Where this note connects.
Payment gone wrong — the four failures and the single one a record can help repair
Payments — what the twelve operators state about the coin in their own pages
