Laeserin on Nostr: GM. Devs, here is your daily reminder to add payment targets to your clients. Now, ...

GM. Devs, here is your daily reminder to add payment targets to your clients.
Now, with on-Nostr spec.

quoting
naddr1qv…89e5

# NIP-A3

## payto: Payment Targets (RFC-8905)

### Event Kind

This NIP defines `kind:10133` for payment target events. This kind is **replaceable**.

`optional` `author:atxmj`

This NIP standardizes payment and tip invocations using the [RFC-8905 (payto:) URI scheme](https://www.rfc-editor.org/rfc/rfc8905.html) for payment targets.

### Broadcasting

Clients *may* allow users to specify payment targets consisting of `type` and `authority` values to generate a kind `10133` event with `payto` tags for payment or tip invocations.

**Client Implementation:**
1. Allow users to input `type` and `authority` pairs
2. Validate inputs according to the rules below
3. Optionally warn users if a `type` is not recognized (but allow submission)
4. Broadcast the event with `payto` tags

#### Tag Format

Payment targets are specified using `payto` tags with the following structure:

```text
["payto", "", "", "", "", ...]
```

Where:
- The first element is always the literal string `"payto"`
- The second element is the payment `type` (e.g., `"bitcoin"`, `"lightning"`)
- The third element is the `authority` (e.g., address, username)
- Additional elements are optional and reserved for future RFC-8905 features

Clients **must** understand elements 0–2; they **may ignore** any additional elements for forward compatibility.

#### Validation

- `type`: Lowercase letters (a-z), digits (0-9), and hyphens (-). Types are case-insensitive; normalize to lowercase.
- `authority`: URL-safe; URL-encode special characters. Format depends on the payment system.
- Clients may perform additional payment-system-specific validation for recognized types.

### Broadcasting Example

```json
{
"pubkey": "afc93622eb4d79c0fb75e56e0c14553f7214b0a466abeba14cb38968c6755e6a",
"kind": 10133,
"content": "",
"tags": [
["payto", "bitcoin", "bc1qxq66e0t8d7ugdecwnmv58e90tpry23nc84pg9k"],
["payto", "nano", "nano_1dctqbmqxfppo9pswbm6kg9d4s4mbraqn8i4m7ob9gnzz91aurmuho48jx3c"],
["payto", "unknowntype", "l7tbta5b9xze6ckkfc99uohzxd009b0r"]
],
...
}
```

### Recommended Payment Target Types

| Payment Target Type | Long Stylization | Short Stylization | Symbol | References |
| :------------------ | :---------------- | :---------------- | :----- | :--------- |
| bitcoin | Bitcoin | BTC | ₿ | https://bitcoin.design/ |
| cashme | Cash App | Cash App | $,£ | https://cash.app/press |
| ethereum | Ethereum | ETH | Ξ | https://ethereum.org/assets/#brand |
| lightning | Lightning Network | LBTC | 丰 | https://github.com/shocknet/bitcoin-lightning-logo |
| monero | Monero | XMR | ɱ | https://www.getmonero.org/press-kit/ |
| nano | Nano | XNO | Ӿ | https://nano.org/en/currency |
| revolut | Revolut | Revolut | N/A | https://revolut.me |
| venmo | Venmo | Venmo | $ | https://venmo.com/pay |

### Observation

For each `payto` tag in kind `10133` events, clients *should* assemble a `payto:///` URI and render it as a button or link.

**Client Implementation:**
1. Parse each `payto` tag from the event
2. Optionally validate `type` and `authority` fields and filter invalid tags
3. Assemble full `payto:///` URIs
4. For **recognized** types, render with associated icons and stylization from the table above
5. For **unrecognized** types, either ignore or use generic stylization
6. If multiple targets exist, render the first one, all of them, or a dropdown selector

### Observation Example

```json
{
"pubkey": "afc93622eb4d79c0fb75e56e0c14553f7214b0a466abeba14cb38968c6755e6a",
"kind": 10133,
"content": "",
"tags": [
["payto", "bitcoin", "bc1qxq66e0t8d7ugdecwnmv58e90tpry23nc84pg9k"],
["payto", "nano", "nano_1dctqbmqxfppo9pswbm6kg9d4s4mbraqn8i4m7ob9gnzz91aurmuho48jx3c"],
["payto", "unknowntype", "l7tbta5b9xze6ckkfc99uohzxd009b0r"]
],
...
}
```

Assembled URIs:
- `payto://bitcoin/bc1qxq66e0t8d7ugdecwnmv58e90tpry23nc84pg9k` (recognized)
- `payto://nano/nano_1dctqbmqxfppo9pswbm6kg9d4s4mbraqn8i4m7ob9gnzz91aurmuho48jx3c` (recognized)
- `payto://unknowntype/l7tbta5b9xze6ckkfc99uohzxd009b0r` (unrecognized)

## Implementation Notes

### Integration with NIP-57 Zaps

Clients may use `payto` lightning entries as an alternative or complement to `lud16` for zap functionality. The `authority` field should contain a Lightning address (e.g., `user@wallet.example.com`) or LNURL.

Example:

```json
[
{
"kind": 0,
"content": "{\"lud16\":\"user@wallet.example.com\"}",
"pubkey": "..."
},
{
"kind": 10133,
"content": "",
"tags": [
["payto", "lightning", "user@wallet.example.com"],
["payto", "bitcoin", "bc1q..."]
],
"pubkey": "..."
}
]
```