Enable private payments

Done once. After this, anyone who knows your ordinary wallet address can send you a private payment — you never have to send them a key, a file or a code.

signs Your wallet signs one message. It authorises no payment and cannot move funds — it only derives your keys.
publishes Only the public half goes on chain: it lets people pay you, and nothing else. It cannot read or spend anything.
keeps The private half never leaves this tab and is not stored anywhere — it is recomputed from your wallet whenever you open /receive/.
costs About 0.01 SOL of account rent, refundable if you ever close the entry. Two transactions: your key is 1216 bytes and does not fit in one.
Your wallet may say it cannot simulate this. That is expected.

The transaction goes to the network selected at the top of this page. Your wallet only signs it — but it previews transactions against whichever network it is set to, and if that is a different one it finds nothing there and warns you.

To make the preview match, switch your wallet to the same network. In Phantom that is Settings → Developer Settings → Testnet Mode.

What becomes public is that this wallet accepts private payments. The payments themselves stay unlinkable: the chain cannot tell which deposit paid you, nor read the amount or the note sealed inside it.